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The Nooksack Valley Field Trip A Classic Excursion in Pacific Northwest Geology J. Figge 2009 This document is designed to be viewed in a “two page” format. To display in this format, choose “2-page view” under “Page Display” from the “View” menu The Nooksack Valley Field Trip A Classic Excursion in Pacific Northwest Geology Geology / Science 111 North Seattle Community College J. Figge 2009 All Parts of this work, as an electronic file or as a paper document, including all text, illustrations and diagrams, except where otherwise noted, are protected under US and International Copyright Laws. No part of this Book may be copied, by electronic or other means, including the posting of parts of this work the Internet, without the expressed written permission of the author and publisher. All Rights Reserved. © John Figge 2009 This document was prepared for the exclusive use of students enrolled in Geology / Science 111, at North Seattle Community College, to whom it is provided as part of that body of academic coursework. This document should be retained by the student, or destroyed after use. This document should not be made available for purchase in any form, or under any circumstances. By accepting this document, students agree to the conditions for its use, as detailed on this page. Neither the author nor the publisher receive any compensation from the limited distribution of this document. © John Figge 2009 Cover Image: Mt. Shuksan from Artists Point, Mt. Baker Highway The Nooksack Valley Field Trip A Classic Excursion in Pacific Northwest Geology J. Figge 2009 The Nooksack Valley Field Trip Introduction: British Columbia The Nooksack Valley trip is one of the true Washington State “classic” field trips in Pacific Northwest Geology. It includes a remarkable diversity of rock North Fork types, and a selection of rocks which illustrate much of the course of regional geologic history Nooksack River Mt. Shuksan here. These are featured in a truly spectacular setting along the northern flanks of Mount Baker, the northernmost of the Cascade VolMiddle Fork Mt. Baker canoes of Washington. Many would offer that this represents one of the true “world class” Twin Bellingham field trips in Pacific Northwest geology. sisters Mtn The Nooksack River is the northernmost of the rivers flowing west off the Washington South Fork Cascades. It is a drainage of modest proportions, extending about 60 miles (100 km) from the tidewaters of Bellingham Bay to a crest on map area Skagit River the western Cascades. It lies nestled between the much larger drainages of the Fraser River to the north, and the Skagit River to the south, and is a province of much more limited extent in comparison. None the less, it is one of the most geologically interesting settings in the Pacific Northwest, and one of the most spectacular montane settings in North America. For these reasons, it has long been a favorite locale for geologic excursions. The Nooksack River has its principal origins in the glaciers which mantle the north sides of Mt. Baker and Mt. Shuksan, two large mountains which dominate the northwestern Cascades here. The main course of the river is the North Fork, which extends east up a valley just 10 km (6 miles) south of the International Boundary. The South and Middle Forks of the river drain the west side of Mt. Baker, and the Twin Sisters Mountain, an important sub-range to the west. The town of Deming, a major settlement in the valley, lies just below the confluence of these tributaries. It is a population of about 200 people. Upstream, settlements on the North Fork include the towns of Maple Falls and Glacier. The name of the valley, taken from the indigenous peoples, means “people of the Bracken Fern” - a staple of the Nooksack diet. The North Fork valley is served by State Highway 542, the Mount Baker Highway. This road ascends the North Fork and climbs to Heather Meadows and Austin Pass, at the Mount Baker Ski Area. For the spectacular views of Mt. Baker, Mt. Shuksan and the North Cascades, it is considered one of the most scenic highways in North America. The trip is best done in late summer and fall, when the road is open to Austin Pass. Road information is available at the Snoqualmie-Mt. Baker National Forest website. The Nooksack Valley Field Trip samples from four distinctive regional geologic units. The oldest of these is the Chilliwack Terrane, a Paleozoic island-arc complex which occupies the southern end of the larger Insular Belt. These rocks (Left) Mount Baker from Artists Point were accreted (added) to the continental margin in midCretaceous time, about 120 million years ago. Also featured are rocks of the Northwest Cascades System, a belt of oceanic mélange-type rocks which were obducted (overthrust) onto the continent about 90 million years ago. These rocks may have their origins along the southern coast of Oregon, or northern California. The route also visits an outcrop of the Tertiary Chuckanut Sandstone, part of an extensive sedimentary cover which blanketed the province in Mid to Late Eocene time. Finally, the tour includes an illustrative sampling of rocks from the Quaternary Mt. Baker Volcano, which crowns the modern range. (Left) “Bear” in an outcrop of Darrington Phyllite, below the Mt. Baker Ski Area Table of Contents Introduction The Geology of the Northwest Cascades Region............................................................................................2 The Chilliwack Terrane.......................................................................................................................7 The Nooksack Group...........................................................................................................................9 The Northwest Cascades System.......................................................................................................11 The Chuckanut Formation.................................................................................................................13 Quaternary Volcanics and the Mt. Baker Volcano.............................................................................15 Pleistocene Glaciation.......................................................................................................................18 A Brief History of the Nooksack Region.......................................................................................................21 The Modern Setting of the Nooksack Valley.................................................................................................24 The Nooksack Valley Field Trip.................................................................................................................28 Stop 1: Rocks of the Northwest Cascades Belt. (Shuksan Greenschist, Darrington Phyllite) ....................29 Stop 2: Rocks of the Twin Sisters Mountain (Dunite) , the Wickersham Valley...........................................31 Stop 3: Rocks of the Chilliwack Terrane (Chilliwack Limestone)...............................................................35 Stop 4: Rocks of the Chuckanut Formation (Siltstone) ................................................................................37 Stop 5: Geologic Cataclysms on the North Fork (Glacier, Lunch) .............................................................39 Stop 6: Rocks of the Nooksack Group (Siltstone).........................................................................................41 Stop 7: Mount Baker, Mount Shuksan, Glacial Processes (Austin Pass) ....................................................45 A Final Note From Your Instructor................................................................................................................51 Millions of Years Ago Era Period Modern Peak of Mt. Baker 0 Miocene Cenozoic Oligocene Eocene Start Pleistocene Ice Ages Start uplift of the modern Cascade Mountains Chuckanut Formation accumulates Paleocene Accretion of the Melange Belts Cretaceous 100 Rifting and Transport of the Melange Belts Nooksack Group accumulates on the Chilliwack Terrane Accretion of the Insular Belt Mesozoic Jurassic 200 The Chilliwack Terrane and the Insular Belt are probably amalgamated by this date Triassic Permian 300 Carboniferous Development of the other terranes of the Insular Belt Development of the Chilliwack Terrane Devonian 400 Paleozoic ? Silurian Ordovician 500 Cambrian Figure 1: Geologic time-line, along with major events in the evolution of the Mount Baker region. 1 Insular Belt Terrane Olympic Coast Belt Intermontane Belt Terrane ? Melange Belt Terranes ? ? North America ? ? (Covered) ? Figure 2: The major accreted terrane-belts of Washington State and southern British Columbia. Dashed lines are hidden contacts. The central Columbia Basin is covered in younger basalt flows. Arrow points to the Nooksack Valley The Geology of the Northwest Cascades Region The Nooksack Valley hosts a remarkable diversity of rock types, reflecting a long and sometimes complex history of geologic evolution. That course of evolution, as with that of the broader Pacific Northwest, includes the accretion (addition) of a number of “terrane” units to the western margin of the continent here. Those “terranes’ were largely island groups from the ancestral Pacific Basin, brought to our shores by the processes of plate tectonics, or sections of oceanfloor rock which were similarly acquired. These “accreted terranes” comprise the deep “basement” rocks across the entire Pacific Northwest. The oldest rocks in the Nooksack Valley are those of the Chilliwack Terrane, the remains of an ancient island group dating from Early Paleozoic time. This island chain was probably amalgamated with the larger “Insular Belt” terranes by Jurassic time, occupying the southern end of that “megaterrane” belt. In Early Cretaceous time (about 140 million years ago), that belt hosted an episode of island-arc magmatism known as the Gambier Arc. Marine sediments derived from these volcanoes are preserved on the Chilliwack Terrane, in a section known as the Nooksack Group. These rocks were all accreted to the continental margin in mid-Cretaceous time, about 115 million years ago. 2 Tomyhoi Peak Black Mtn Red Mtn. To Bellingham Sumas Mtn. Mt. Larrabee Church Mtn Goat Mtn Maple Falls Mt. Sefrit Glacier Mt. Shuksan Deming Mt. Baker Baker Chuckanut Acme Melange Belts Nooksack Twin Sisters Mtn Loomis Mtn LakeWhatcom Mt. Baker Twin Sisters Mt. Baker Loomis Mtn NooksackValley 3 Twin Sisters Chilliwack WickershamValley Figure 3: (Top) Map showing the major geologic units in the Mt. Baker region. Barbed lines are thrust faults, with the barbs on the upper plate. (Lower) Crosssections (A-A’, B-B’) from the map above. All contacts are thrust faults. Mt. Baker is a more recent feature. Map Area Mt. Shuksan Fraser Fault Chuckanut Formation Olympic Coast Belt Chuckanut and Swauk Formations Swauk Formation Olympic Coast Belt Methow Region Insular and Melange Belt Terranes 50 Ma Fraser Fault 40 Ma Figure 4: Maps illustrating the offset of terrane units, along with elements of the Swauk and Chuckanut Formations, by the Fraser Fault between 50 and 40 million years ago. Also shown is the emplacement of the Olympic Coast Belt, which was thrust underneath the southern end of Vancouver Island. The next “package” of rocks to be added to the region is a group known as the Melange Belts. These are dominantly sections of oceanic crust, along with their sea-floor sediments, fragments of continental crust, sections of mantle rocks, and a variety of other broadly oceanic components. In a unique development, these rocks were obducted (thrust over the top of) over the continent, across the southern end of the Insular Belt. The resulting “stack” of terrane units here is known as the “Northwest Cascades System.” These “thrust sheets” are separated by low-angle thrust faults, reflecting movement to the north. In early Tertiary time this accreted province hosted a major river system, during a period of rapid coastal subsidence. This resulted in the accumulation of a truly remarkable thickness of non-marine sediments along the continental margin. In places, this represents some 5 km (15,000 feet) of deposition. Locally, these rocks are known as the Chuckanut Formation. The Chuckanut is displaced from its original headwaters in the Swauk Formation east of Snoqualmie Pass, 4 Figure 5: (Right) Map showing the evolution of the Cascade Arc over time. The Early Cascade Arc is marked by plutonic rocks, the remnants of volcanoes which erupted between 36 and 7 Ma. Between 7 and 5 Ma, the trace of the arc shifted west, into the modern Baker - Garibaldi - Mt. Meager Belt. Trace of Recent (5 - 0 Ma) Cascade Arc Trace of Early (36-7 Ma) Cascade Arc Pemberton Plutons Mt. Meager Chilliwack Batholith Mt. Garibaldi Mt. Baker Modern Volcanoes Glacier Peak Older Cascade Arc Plutons separated by 145 km of right-lateral (west side to the north) displacement on the ~50 – 40 Ma Fraser Fault. This fault was located just east of the modern headwaters of the Nooksack River. This episode concluded with the accretion of the Olympic Coast Belt to the west, a section of oceanic plate which was thrust beneath the southern end of Vancouver Island. Over most of the last 36 million years, the volcanoes of the modern Cascade Arc have been erupting to the east of this area. The deep plutonic “roots” of those volcanoes are preserved as the Chilliwack Batholith, which covers much of the Ozette and Hoh Crescent Basalts Melange Formations Melange Belts Chilliwack Terrane ? Igenous and Metamorphic Province Cascade Mountains Olympic Mountains Puget Basin Figure 6 (Above) Diagram illustrating the recent uplift of the modern Olympic and Cascade Mountains. This has happened over the last five million years, as a result of compression along the continental margin. The Puget Basin is the central trough beween these two folds. 5 region between the Nooksack and the upper Skagit River. The Cascade Arc did not move into what is now the Nooksack drainage until about 5-7 million years ago, about the time that the modern Cascade Range began to rise. Mount Baker is only the most recent in a long lineage of volcanoes which have grown here over the last several million years. It is probably not much more than 50,000 years old. Uplift of the modern Cascade and Olympic Mountains commenced about 5 million years ago, developing as a set of north-south trending folds which have resulted from compression of the continental margin. The Puget -Georgia Basin is the trough between those two folds. Over the last two million years, this region has hosted a succession of episodes of continental glaciation, as the Cordilleran Ice Cap has periodically advanced south out of Canada. Along with various episodes of local alpine glaciation, these events sculpted the region to its modern form. The continental icecap last retreated about 12,000 years ago, from whence the modern ecosystems have developed. Cordilleran Ice Cap Nooksack Valley Juan De Fuca Lobe Glacier Puget Lobe Glacier Figure 7 (Above) Illustration showing the maximum extent of the Cordilleran Ice Cap during the last glacial episode, about 14,000 years ago. At this date, the Nooksack drainage is entirely mantled in ice. 6 Figure 8: (Right) Map showing the Chilliwack Terrane as the southern end of the Insular Belt Terranes. Also shown are the Nooksack Group (Gambier) deposits which accumulated across this island belt in Early Cretaceous time. The southern extent of the Chilliwack Terrane is uncertain. It is overthrust by the rocks of the Melange Belts (not shown), and is largerly covered south of the Skagit River. Insular Belt Terranes Nooksack Group Volcanics Figure 9 (Below Right) Timeline showing the evolution of the Chilliwack Terrane Chilliwack Terrane Millions of years Ago The Chilliwack Terrane The Chilliwack Terrane is the remains of an ancient island group which developed in the paleopacific basin over Paleozoic time. It takes its name from the town of Chilliwack in southeastern British Columbia, but the terrane extends south well into Washington State. The earliest rocks of this unit are pre-Mid-Devonian in age, known as the Sumas Mountain Subgroup. A prominent limestone section characterizes the Carboniferous Red Mountain Subgroup; while a volcanic and volcaniclastic section of basaltic to andesitic island-arc rocks dominate the Permian Black Mountain Subgroup. The Chilliwack Terrane is the southernmost component in the larger Insular Belt, an amalgamation of island-arc terranes which was accreted to the continental margin in mid-Cretaceous time. The boundary between the Chilliwack and terranes to the north is obscured, so we can’t be certain of when they were amalgamated. The Chilliwack is depositionally overlain by the Late Triassic to Early Jurassic Cultus Formation, a sequence of volcanic sediments which suggest an offshore island slope or deep-water setting. The Chilliwack and Cultus are in turn overlain by sediments of the Early Cretaceous Nooksack Group, as described below. 7 100 Cretaceous Insular Belt Accreted Jurassic 200 Triassic Permian 300 400 Carbon. Red Mountain Subgroup Devonian Sumas Mtn. Subgroup Silurian Ordo. 500 Cultus Formation Black Mountain Subgroup Cam. Figure 10 (Above) Rocks of the Chilliwack Group, at an outcrop on Sumas Mountain. These are Permian rocks of the Black Mountain Subgroup. The dark rocks are mafic volcanics. Figure 11 (Right) Rocks of the Chilliwack Group, at an outcrop high on Sauk Mountain. Here, you can see the transition from dominantly volcanic rocks to a sedimentary breccia. This is part of the Red Mountain subgroup, the same part visited at stop 3 on this trip. 8 The Nooksack Group The Nooksack Group of volcanically-derived sediments and minor volcanic rocks accumulated on the Chilliwack Terrane in Early Cretaceous time, before that terrane was accreted to the continental margin. At that time it was probably an offshore island belt, not unlike the modern islands of Japan. These volcanic rocks were part of the Gambier Arc, an island-arc which developed across the Insular Belt islands in Early Cretaceous time. Much of the Nooksack Group appears to be an extensive submarine debris-fan which accumulated at the base of a large basaltic to andesitic volcano. These are largely fine-grained volcanically-derived siltstones and sandstones, often reflecting deposition by debris-flow (turbidite) avalanches. In places, this unit is nearly 2 km thick. Figure 12 (Above) Rocks of the Nooksack Group, exposed high on Skyline Divide, on the north side of Mt. Baker. Here you can see the distinctive bedding pattern in these rocks. These are turbidite flows, submarine avalanche deposits from the slopes of a volcanic debris fan. The beds show the classic fining-upward sequence characteristic of these deposits. 9 Figure 13 (Above) Fossil clams and belemnites of the Nooksack Group, on Skyline Divide at 7,000 feet. Figure 14 (Below) Belemnites, in a polished block of Nooksack Group sediments. Photo by George Mustoe. Figure 15 (Right) Clam fossils from the Nooksack Group. Common species include Buccia and Pina Clams. These are often found in growth position, indicating that they were buried alive. 10 Figure 16 (Right) Map showing the distribution of the Melanage Belt rocks in western Washington. The red area is that of the Northwest Cascades Belt rocks, as visited on this trip. The purple and yellow areas are rocks of the western and eastern Melange Belts, which are part of this “package” Bellingham High-grade igneous and metamorphic rocks of the North Cascades “Core” region Fraser Fault These rocks were thrust over the top of the continent, along low-angle thrust faults. Seattle Northwest Cascades Belt Rocks Chilliwack Terrane Rocks The Northwest Cascades Belt The Northwest Cascades Belt is the northernmost belt in a group of terranes known as the “Melange Belts”. These are terranes of broadly oceanic affinity, but consist largely of fragmental rock sections, often extensively deformed, and rarely continuous over any distance. The word “mélange” is French, meaning a “mix” – as in a mixed salad. It is an appropriate description. The Northwest Cascades Belt is the only one of these belts which contains coherent lithologies which can be traced for some distance. These rocks principally include a suite of oceanic crust (the Shuksan Greenschist) and its pelitic (oceanfloor mud) cover (the Darrington Phyllite). These rocks were metamorphosed at blueschist facies, a condition unique to subduction-zone settings. It is thought that these rocks were exhumed from a subduction zone along the northern California or southern Oregon Coast about 120 million years ago, consequent to a change in ocean-plate configurations. In this process, sections of upper mantle rock (e.g. the Twin Sisters Dunite) were also exhumed from this deep setting. This assemblage also includes other varied oceanic rocks, along with fragments of continental gneiss and other lesser components. 11 The Northwest Cascades rocks were carried northward on an oceanic plate, and were apparently “peeled” off the top of the plate when it was subducted beneath the edge of the continent. In the process, these rocks were thrust over the top of the continent (the Chilliwack Terrane) along low-angle thrust faults, probably for hundreds of kilometers. These rocks, along with fragments of the Chilliwack Terrane, are preserved in a distinctive stack of “thrust sheets” known as the Northwest Cascades System. The low-angle thrust faults which define these sheets often contain sections of ultramafic rock, which served to “lubricate” the fault zones. Rocks are obducted across the southern end of this area Pacific Ocean Kula-Farallon Ridge Old Subduction Zone Rocks are rifted off the continental margin and Transported northward Figure 17 (Above) Diagram showing the origins of the Melange Belts Figure 18 (Below Left) The Shuksan Greenschist, at an outcrop along Finny Creek. Hammer gives scale Figure 19 (Below Right) The Darrington Phyllite. Note included quartz. Dime gives scale 12 Figure 20 (Right) Illustration of the interpreted paleogeography of the region during Mid-Eocene time. The Olympic Coast belt has not yet been accreted. Note the large river draining across the province, the source of the widespread sedimentary units which date from this period. The Chuckanut Formation The Chuckanut Formation is an extraordinarily-thick accumulation of non-marine arkose sediments which in part reflect deposition by a major river system. These sediments accumulated on a rapidly-subsiding coastal plain in Eocene time, between 55 and 37 million years ago. They consist of siltstones, sandstones and conglomerates, quartzo-feldspathic sediments derived from igneous or metamorphic rocks. 40 The oldest rocks of the Chuckanut Formation accumulated between 55 and 48 million years ago, and are known as the Bellingham Bay Member. These rocks are equivalent to the Swauk Formation on the east side of Snoqualmie Pass. About 48 million years ago these systems were separated as the west side moved north about 145 km (90 miles) along the Fraser Fault. The Bellingham Bay Member was folded in this process, and eroded back to base level before subsequent deposition. Subsequent members of the Chuckanut Formation were removed from that original source area. The Padden and Slide Members overlie the Bellingham Bay Member, consisting largely of re-worked deposits. Above, minor members include sediments of more local derivation. 13 E O C E N E Warnick Bald Mtn Maple Falls mbrs Padden Member Folding and Erosion 50 Bellingham Bay Member Period of Movement on the Fraser Fault Oxbow LAke coal and fine sediments Floodplain Bank Deposits Bar deposits Figure 21 (Above) Depositional setting of the Chuckanut Formation. Drawing by George Mustoe. Figure 22 (Left) Trackways in the Chuckanut Formation, the footprints of large herbivores typical of a moist paratropical environment. Photo by George Mustoe Figure 23 (Below) Unconformable contact between the Bellingham Bay and Padden Members of the Chuckanut Formation. This shows that rocks of the Bellingham Bay Formation were folded and eroded prior to the deposition of the Padden Member. This episode of deformation dates from ~50 to 48 Ma, and probably reflects the onset of faulting on the Fraser Fault System. Padden Member The Chuckanut contains an abundant fossil record. Early members reflect a warm, lush, paratropical setting, the dominant species being palm trees. Later members reflect a cooling trend leading to a more temperate climate. All of these rocks reflect deposition on a broad subsiding coastal floodplain, the site of a substantial river draining to the ocean some distance to the southwest of this area. bellingham Bay Member 14 North American Plate Explorer Ridge Explorer Plate Figure 24: Map showing the modern plate -tectonic setting of the Pacific Northwest, with the Juan De Fuca Plate being subducted beneath the western margin of the continent. The Juan De Fuca Plate moves to the east, North America moves to the west. This supports the Cascade Volcanic Arc to the east.Yellow areas are older Cascade Arc Volcanics. Red triangles are the modern Cascade Volcanoes. Mt. Baker Juan De Fuca Ridge Juan De Fuca Plate Gorda Ridge Gorda Plate Pacific Plate Mount Baker and The Rocks of the Cascade Arc The Juan De Fuca Plate has been subducting beneath the continent here for some 37 million years, supporting magmatism of the Cascade Arc. Over most of that period, the local volcanoes rarely rose more than 1-2 km (3-6,000 feet) above a surrounding lowland province. While there was a modest hydrologic divide where the modern range now stands, the Cascade Mountains did not start rising until about 5 million years ago. Prior to that date, the volcanoes rose as isolated features on the landscape. Prior to the uplift of the modern range, magmatism of the Cascade Arc was largely concentrated to the east of the Nooksack region. The large composite Chilliwack Batholith contains intrusions ranging from 36 – 7 Ma, the plutonic “roots” of a succession of volcanoes which developed at upper levels. Granitic rocks occur at the very headwaters of the Nooksack, The westward migration of the arc into the modern Mount Baker area is illustrated by the ~4 ma Lake Ann Stock, a small granodiorite body which intrudes the rocks of Shuksan Arm, just east of Austin Pass. Uplift of the modern range has caused erosion of the upper levels, exposing the granitic stock at depth. 15 Figure 25 (Above) Mount Baker from the east, showing the location of the 1.1 Ma Kulshan Caldera. This feature developed long before the modern peak. Black Buttes Volcano Figure 26 (Right) Mt. Baker from the north. Arrow points to the former volcanic cone of the Black Buttes. These are the remnants of a volcano which developed here perhaps 300,000 years ago. Several volcanoes have likely risen where modern Mt. Baker now stands, the last version being the Black Buttes, the eroded remains of a former cone just west of the modern peak. Over the last two million years, those recurring volcanoes were eroded by a succession of local and continental glacial episodes, likely erasing most evidence for the earliest eruptive events. Among those events was a large explosion caldera (crater), which erupted on a ridge northeast of the modern peak about 1 million years ago. Known as the Kulshan Caldera, it likely erupted during glacial times. Ash from this eruption can be found east of Tacoma, preserved on the floor of Lake Tapps. The modern cone of Mt. Baker was probably constructed in large part over the last 50,000 years. Given its level of activity, it doesn’t appear to have weathered more than one episode of continental glaciation. It is composed largely of andesite flows which emanated from the summit area. In recent times (1854?) a new vent was formed on the south side of the peak, known as Sherman Crater. Cinder cones have erupted lower on the south side of the peak over the last couple hundred years, and pyroclastic flows have occurred in historical times. Like the rest of our volcanoes, it has a propensity for producing large-scale lahars, or volcanic mudflows. These mudflows have swept down most of the major valleys, reaching as far as Puget Sound and the Georgia Strait. 16 17 Figure 27 (Left, Top) Mount Baker from Sauk Mountain, showing its classic conical form. Figure 28 (Left, Bottom) Volcanic hazards of the Mt. Baker Area, from the U.S. Geological Survey. Figure 29 (Right, top) Lahar (volcanic mudflow) deposits along the North Fork Nooksack River, near Glacier. Deposits like this are found in the Nooksack and Skagit Rivers, extending all the way to tidewater. There are no warning systems in place, should events of this nature occur. Pleistocene Glaciation Over the last two million years this region has been repeatedly inundated by both continental and alpine-scale glaciers which have developed on a recurring basis. How many episodes are represented remains uncertain, but it probably numbers in the dozens. Between those glacial episodes were non-glacial or high-glacial periods much as exist today. Owing to their elevation, volcanoes the size of Mt. Baker were probably mantled in ice over much of these periods. Figure 30 (Left) Mount Shuksan, from the Mt. Baker Ski Area. The Hanging Glacier descends from the upper shelf, and cascades down an icefall into a cliff. Periodically, boxcar-sized chunks of ice crash down into the valley below. The name Shuksan is a native term for “Roaring Mountain”. The North Cascades are the most heavily glaciated range in the US, south of Alaska. Most of these are melting rapidly, and will disappear over the next century. 18 Fraser River Figure 31 (Right) Map showing ice-marginal drainage channels through the foothills east of the Puget Sound. These were formed as advancing ice (dotted line) dammed these river drainages. Nooksack River Columbia Spillway Wickersham Spillway Figure 32 (Below Right) Column showing the glacial deposits of the Puget Basin, a record of the last six episodes of continental glaciation here. Skagit River Sauk Spillway Stilliguamish River While there were likely episodes of local alpine glaciation which did not develop into continental-scale icecaps, their independent effects are difficult to gauge. In the most recent episode of continental glaciation, the continental icecap eventually mantled most of this region, covering all but the highest mountain summits. At lower levels, ice descended the valleys to merge with the Puget Lobe to the west. At upper levels, ice flowed over the low passes into the Skagit Basin to the south. The most recent episode of glaciation occurred locally as ice in the mountains grew between 25,000 and 21,000 years ago. Those alpine glaciers extended much of the way down the Nooksack Valley, but were retreating by 20,000 years ago, when the continental icecap last advanced south across the international boundary. As it did, lowland ice dammed the Fraser River, which was an ice-free corridor at the time. The impounded waters of this lake rose until they overtopped the divide to the south, and spilled down the Columbia Valley into the lower Nooksack drainage. The Columbia Valley Spillway connects the Fraser and Nooksack drainages. As the ice advanced to the south, it eventually dammed the Nooksack River, forming a large lake in the recently-deglaciated valley. That lake rose until it overtopped a low divide to the south, and drained to the Skagit Valley below. That drainage channel is the Wickersham Coulee. Other ice-marginal drainage channels also temporarily included Lake Whatcom and Samish Lake. By 19 Fraser Glaciation Possession Glaciation Double Bluff Glaciation Salmon Springs Glaciation Stuck Glaciation Orting Glaciation Figure 33 (Above) Illustration showing the maxium extent of continental glaciation during the last glacial episode, about 14,000 years ago. Base illustration from Google Earth. 15,000 years ago, advancing ice had filled in the Nooksack Valleys, and was spilling into the drainage from the north. By 14,000 years ago, the glacial maximum, the region was completely mantled in ice. After that date, continental ice retreated rapidly from the region. While the lowlands were largely ice-free by 13,000 years ago, a brief re-advance of the icecap stalled the final retreat until about 11,000 years ago. It took another couple thousand years for the land to re-bound from the weight of the ice, rising as much as 100 m (300 feet) in the process. By that date, the earliest known human inhabitants had appeared on the scene. Figure 34 (Right) Klawatti Peak, a heavilyglaciated mountain in the North Cascades. This is a remnant of what was once a great ice sheet which covered the northern end of the range during the last glacial maximum. South of Alaska, 90 per cent of the glaciers in the US are located here in Washington State. 20 Figure 35 (Right) Joe Gailbraith heads up the Middle Fork Nooksack during the Marathon of 1910. Figure 36 (Below Right) The Lone Jack Mine, built on the cliffs above Silesia Creek. The Lone Jack prospect was discovered in 1896, setting off a gold rush to the area. It was one of only a handful of sites eventually developed. History The Nooksack Valley enjoys a colorful history dating from the earliest days of settlement. The valley was originally home to the Nooksack Indians, one of the oldest indigenous groups in the Puget Sound region. These peoples may have their origins in the Middle Thompson cultures of British Columbia, and may have settled within a few thousand years after the retreat of the continental icecap. Most of the tribe succumbed to epidemics as European explorers and traders advanced into the area, particularly during the 1830’s. The town of Bellingham was founded in the late 1850’s, sited to take advantage of coal deposits in the Chuckanut Formation. The earliest explorations of the region date from the late 1850’s, as part of the International Boundary Survey. The headwater regions were not thoroughly examined until the 1890’s, first as part of a road-building project, then as host to a local gold rush. The discovery of gold at the Lone Jack prospect on Swamp Creek in 1897 sparked a rush which brought some 3,000 prospectors to the region, most of whom left after a year or two. Mining interests persisted, sporadically, over the next sixty years. Mining and development interests advanced rail service to Glacier by 1903, with a serviceable 21 road as far as Maple Falls. As part of a program to increase tourism, the local “Mount Baker Club” hosted a series of marathon races in 1910, 11 and 12 - quite arguably the most demanding sporting events in regional history. Contestants took the train to Glacier, or a car up the Middle Fork Road, and ran up to the summit of Mount Baker before re-tracing their routes back to town. These were all-out competitions of speeding trains, racing cars, and truly fearless runners. The events were cancelled after various near-death experiences in the 1912 competition. The Nooksack Valley was largely settled by Dutch immigrants before the turn of the century, followed by German settlers, and later by a more diverse population. Many of the geographic names reflect this Dutch heritage, as does the culture of many of the small towns. Dairy farming has been a major enterprise here, supported by a damp maritime climate and extensive floodplain areas. Figure 37 (Above) The Mount Baker Lodge, in its hayday. Underwritten by the people of Bellingham, it was intended to popularize the region for their economic benefit. Figure 38 (Right) Interior of the Mount Baker Lodge, a 5-star luxury hotel. The motif is Native American, construction was from native Cedar. 22 In the late 1920’s the same Mount Baker Club organized public support for a luxury lodge to be built in the Heather Meadows area, and an extension of the State Highway to that locale. The Mount Baker Lodge was built, and became a very popular destination with affluent tourists of that time. Business at the lodge was hit hard by the onset of the depression, but suffered far more when it burned to the ground in 1931, a victim of all-cedar construction and a faulty electrical system. A few out-buildings were operated as a lodge through the 1940’s, but the grandeur of the original building was lost forever. In later years, the buildings were demolished, or became part of the modern ski-area facility. A few of the original structures still remain. The valley and its tributaries were logged extensively over the 1940’s, 50’s and 60’s, supporting the timber culture which is still strong in towns like Deming (home of the annual Deming Logging Show). Harvests were restricted to more sustainable limits in the late 70’s and 80’s, which had a significant effect on the local economy. While timber harvesting continues on a more limited scale, employment in this field has dropped appreciably. At the same time, the popularity and scope of the Mt. Baker Ski Area has grown considerably, catering to both American and Canadian interests. Over strong local objections, the uppermost headwaters of the Nooksack North Fork were included in the North Cascades National Park in 1963. In the 1980’s, a large portion of the upper drainage was set aside as the Mount Baker Wilderness, consisting of the high country environs of Mount Baker and the Twin Sisters Mountain, and subalpine to alpine regions north of the river. In contrast to its earlier role as the local timber broker, the Forest Service now largely manages the North Fork for various forms of recreation. Figure 39 (Right) Touring on the Mount Baker Highway, circa 1927. Photo from the Whatcom County Museum of History 23 The Nooksack Valley Today The modern-day Nooksack Valley is a mix of old and new elements, but still retains the pastoral, forest and montane settings which are its fundamental character. In the summer, the region hosts hikers, climbers, campers and tourists from around the world, offering some of the most spectacular mountain scenery to be had anywhere. In the winter, it draws skiers and snowboarders to the ski area at Heather Meadows, while attracting cross-country skiers, snowshoers and snowmobile enthusiasts to the back country. It is a popular year-round locale for various forms of recreation, which has become the economic mainstay of the valley. Above the urban center on Puget Sound, the lower portion of the Nooksack is a pastoral setting of farmlands and dairy pastures, not remarkably changed from its character over the last hundred years. Development pressures are forcing that urban center outward, along with growth in the suburban communities. Figure 40 (Above) The Nooksack Valley North Fork. Image by Duroc. Figure 41 (Right) Maple Falls, the major population center in the upper valley. 24 Figure 42 (Above) The town of Glacier, last settlement on the North Fork Road. Figure 43, 44 (Below) Scenes from the Deming Logging Show, and annual event in the town of Deming. This is an international event, celebrating the towns logging heritage. Photos by Duroc (left) and Teecer (right). Above the lowland floodplain, the towns of Deming, Kendall, Maple Falls and Glacier extend up into the mountains. All of these communities have been impacted by the decrease in timber harvesting, Deming to the largest degree. Deming hosts an annual logging rodeo every summer, which is popular on a regional basis. Historically, it has been the major town in the valley, with a current population of about 200. The town of Kendall dates from 1884, and is home to about 160 residents. Maple Falls, the largest town at some 275 people, serves a broad range of interests, with a particular emphasis on recreational activities. It was originally established in the late 1890’s, when it was the end of stagecoach service. The town of Glacier is the highest incorporated settlement, with a population of about 90 people. It too dates from the 1890’s, and enjoyed rail service by 1903. It was originally founded to take advantage of coal deposits on the slopes behind town, but they proved to be of limited extent. It was a major staging center for sporadic gold rushes and persis- 25 Figure 44 (Right) White Church in the town of Deming. Faith-based values run strong in this valley. tent mining development over the early 20th century, but never seems to have coalesced as a coherent community. It is currently distinguished as having the lowest per-capita income of any community in the state. None the less, the town has seen some significant business investments over the last several years. Above the town of Glacier are a myriad of condominium complexes which sprawl across the woodland landscape. These are outside the town limits, on county land. They are a mix of vacation homes and seasonal residences, which are very popular with Canadians to the north. The sale of these properties is a leading economic activity in the upper valley, and appears to be continuing without significant restriction. 26 British Columbia Washington 3 Maple Falls Nooksack River 6 4 Glacier 5 North Fork Nooksack River Mt. Shuksan 7 Deming Mt. Baker Lake Whatcom Bellingham Middle Fork Nooksack Acme 1 Twin Sisters Mtn. 2 South Fork Nooksack River Baker Lake Lake Shannon Skagit River Map Area Burlington Sedro Woolley Figure 46 (Above) Map showing the route and region of the field trip. Numbered stops (red dots) include: Stop 1: Rocks of the Northwest Cascades Belt (Shuksan Greenschist and Darrington Phyllite) Stop 2: The Twin Sisters Dunite (Northwest Cascades Belt) and the Wickersham Valley Stop 3: Limestone of the Chilliwack Terrane, Rocks of the Insular Belt Stop 4: Rocks of the Chuckanut Formation Stop 5: Glacier (Lunch) Stop 6: Rocks of the Nooksack Group (Chilliwack Terrane) Stop 7: Artists Point: Mount Baker, Mt. Shuksan, Glacial Processes 27 Nooksack Valley Field Trip From Seattle (NSCC): 9 Travel north on Interstate 5 about 60 miles from Seattle to the town of Burlington, at the exit for State Route 20. SedroWoolley Burlington Burlington (Pop 6757 ) takes its name from Burlington Vermont, the home town of its founder. Incorporated in 1902, it achieved some notoriety in 1989, when a large shopping mall (Cascade Mall) was constructed here. 20 Mount Vernon Take SR 20 east about five miles to the town of Sedro Woolley. On the east side of town, take State Route 9 north, signed for Sumas. Everett Sedro Woolley (Pop. 10,300) is a contraction of the names of two towns (Sedro, Woolley) which were founded on opposite sides of the river. The two were incorporated in 1898 under the combined name. Sedro is taken from the Spanish name for Cedar, while Woolley took the name of its founder. The large industrial complex in the middle of town was a Bendix ballbearing plant during World War II. Seattle Figure 46 (Above) The Town of Burlington, on the Skagit River Figure 47 (Above Right) Image showing driving route from Seattle to Sedro Woolley. Base image from Google Earth. Figure 48 (Right) Entrance to the town of Sedro-Woolley, Gateway to the North Cascades 28 Take SR 9 north up into the Wickersham Valley. At 78.5 miles from Seattle (NSCC), take the left turn signed for Lake Whatcom (Park Road). About a mile up the road, pull over and park along the side of Mirror Lake. The outcrop is about 100 feet down the road, to the south. To Lake Whatcom Parking Stop 1 Mirror Lake Park Road Highway 9 Figure 49 (Above) Image showing location of Stop 1 at Mirror Lake. Base image from Google Earth, looking north. Stop I: The Shuksan Greenschist and Darrington Phyllite Rocks of the Northwest Cascades Belt There are two rock types in evidence here. One is a green rock, one is black. These are both metamorphic rocks, evidenced by their layered (foliated) fabric, resulting from the planar-parallel alignment of microscopic platy-shaped (e.g. mica-type) minerals. These minerals were produced during the process of metamorphism. The green rock is a variety called a greenstone. Because it has that layered fabric, it is a type of rock known as a schist. Accordingly, it is properly described as a greenschist. The minerals in a greenschist rock develop at temperatures of 200 – 250 C, under several thousand atmospheres of pressure. They develop from a suite of minerals which are typical of volcanic rocks, particularly of basalt. The chemistry of this rock suggests that it is derived from ocean-floor basalts, from a section of oceanic crust. This rock is known as the Shuksan Greenschist, as it was originally studied at the headwaters of the Nooksack River, near Mt. Shuksan. The black rock is a variety called phyllite. The layered fabric and shiny surfaces in phyllite result from the development of microscopic mica crystals during the process of metamorphism. Phyllite develops from the metamorphism of mudstones, under the same conditions as produce greenschist from basalt. Because this phyllite is found in association with sections of oceanic crust (the Shuksan Greenschist), it is a reasonable assumption that this represents the muddy sediments which accumulate on the ocean floor. This rock is known as the Darrington Phyllite, originally studied around the town of Darrington – at the head of the Stilliguamish River. The Shuksan Greenschist and the Darrington Phyllite are part of the Northwest Cascades Belt of terranes, the northern end of a larger belt known as the Melange Belts. These are a collection of rocks which appear to have been broken off the southern coast of Oregon or the northern coast of California, and subsequently added to the continent here. The 29 figure 50 (Right) Outcrop of stop 1. Rock to the right (black) is the Darrington Phyllite. The rock to the left (light green) is the Shuksan Greenschist. The boundary between the two is a fault. Shuksan rocks have a unique chemistry which suggests that they were being subducted along that coastal margin between 120 and 130 million years ago, when that subduction zone was destroyed and exhumed from depth. The Shuksan and Darrington rocks, along with the rest of the Melange Belts, were transported northward on the oceanic plate, and were obducted (thrust over the top of the continent) as they arrived on the southern end of the Insular Belt. These rocks have been thrust over the Chilliwack Terrane along a series of low-angle thrust faults, and may have been thrust several hundred kilometers in the process. Figure 51 (Above) Shuksan Greenschist, metamorphosed ocean-floor basalt. Figure 52 (Above) The Darrington Phyllite, metamorphosed ocean-floor mudstone 30 Return to SR 9 and continue north for several hundred yards to a turn-out on the right side of the road. Stop 2: The Twin Sisters Dunite and the Wickersham Valley The view to the east is of the Twin Sisters Mountain, a distinctly red-colored range of peaks in the late season. Behind the Twin Sisters, the summit of Mt. Baker can be seen. The rock of the Twin Sisters Range is a variety called dunite – a rock comprised almost entirely of the mineral olivine. This is the type of rock which geophysicists tell us comprises the mantle of the Earth, the large volume of material between the crust and the core. Mantle rocks only rarely make it to the surface of the planet, and only when brought up along very deep faults. Usually, they are sheared to rock called serpentinite, a variety often used for ornamental purposes. Only rarely do significant bodies of undeformed rock make it to the surface. The rock is used for refractory purposes, including as furnace linings and as casting sand. Owing to its origins in a high-temperature / high -pressure setting, it is stable under extreme temperatures. In the North Cascades, rocks of this type are frequently found in the low-angle thrust faults between thrust sheets of the Melange Belts. The Twin Sisters Dunite is a very large section of this rock, the largest in the Western Hemisphere – and the second largest in the world. It is located along one of these thrust faults. This rock appears to have been exhumed from depth along with other elements of the Northwest Cascades Belt, as the bottom-most layer in that former subduction zone. Along with the rest of these rocks, it has been thrust over the top of the Chilliwack Terrane. 31 The other feature of note here is the Wickersham Valley itself, an anomalous north-south trending valley between the Nooksack and Skagit Rivers. As described in the introduction, this developed as an ice-marginal channel which drained waters impounded by advancing ice in the Fraser and Nooksack Drainages, carrying that water to the Skagit River. During various stages of glacial advance, many of the valleys here served in this manner. The valley of Lake Whatcom is probably of these origins, as is the narrow valley which connects it with the Wickersham Valley ( visited at Stop 1). The Wickersham spillway was probably formed in the early glacial episodes, and was deepened during subsequent advances. Eventually, this entire region was overrun by the icecap. Figure 53 (Left) The Twin Sisters Mountain, from Stop 2. Mount Baker to the rear. Figure 54 (Right) A sample of Twin Sisters Dunite. Dime gives scale. Figure 55 (Below) The Wickersham Valley, an ice-marginal drainage channel from the Nooksack River Valley south to the Skagit Valley. See figure 31 for map. 32 Continue north on State Route 9, through the towns of Acme and Van Zandt, to meet State Route 542 (the Mount Baker Highway). Acme and Van Zandt are old towns, originally established as Dutch settlers immigrated to the region. Much of the land in this valley has been held in families for generations, which explains the lack of subdivision for housing developments. The valley remains a largely agrarian setting. Turn right (east) on 542, signed for Mount Baker. Pass through the town of Kendall, where Highway 547 Figure 56 (Above) Grocery and gas in the town of Acme. continues north to Sumas. Continue east on the Mount Figure 57 (Below) Illustration showing the route up State Route 542 to stop 3. Base image from Google Earth Baker Highway. Stop 3 Kendall Maple Falls Deming 33 North of Kendall, Highway 547 ascends the Columbia Valley. This is an ice-marginal channel where waters impounded by the advance of the icecap into the Fraser Valley spilled south to the Nooksack. This is known as the Columbia Spillway. Fraser River Columbia Valley Continue east on Highway 542 to the town of Maple Falls. Here, turn north on the Silver Lake Road. Several miles up the road, pull over at the Clausen Quarry. Maple Falls is an unincorporated community with a population a bit less than 300. It is the largest town on the upNooksack River per Nooksack, and displays its German heritage in the local Figure 58 (Above) Image showing the diversion of the Fraser River down the Columbia architecture. Spillway. Base image from Google Earth Figure 59 (Below) Silver lake, photo by Searunner 34 Figure 60 (Above) The Clausen Limestone Quarry on the Silver Lake Road. This pit largely produces aggretate and agricultural lime for the immediate region. There are a number of limestone quarries in this area, tapping the Red Mountain Subgroup of the Chilliwack Terrane. Stop 3: Limestone of the Chilliwack Terrane The rocks being quarried in the Clausen Pit are limestone of the Chilliwack Terrane, from the Carboniferous Red Mountain Subgroup. These rocks are derived from reef-type marine communities which grew around the Chilliwack Islands perhaps 350 million years ago. This is over 200 million years before these rocks were added to the edge of the continent here. At this time the Chilliwack Islands probably lay far out in the Pacific Basin, and were probably not yet amalgamated with the rest of the Insular Belt. These rocks would be accreted to the continental margin about 120 million years ago, in mid- Cretaceous time. The dominant organisms in this limestone are Crinoids, commonly known as “sea-lillies”. Members of this genera still exist. These were most numerous in Mississippian (Late Carboniferous) time, where they occupied the ecologic niche now held by coral species. Great communities of crinoid species filled the shallow waters around the Chilliwack Islands, now converted to limestone. In places, one can see the distinct bulls-eye pattern presented by the fossilized cross-section of their bodies. The limestone quarried here is used for local purposes, for boulders, crushed rock, and as agricultural lime. This is the same limestone which supported the cement industry in Concrete, on the Skagit River. Concrete from that source was used to build the hydroelectric dams on the Skagit River. 35 Figure 61 (Top left) Drawing of a typical crinoid species. Figure 62 (Top Right) A polished section of Chilliwack Limestone, from the quarry at Concrete. Note the prominent crinoid stem cross-sections. Figure 63 (Left) A handsample of limestone from the Chilliwack Group. Return to Maple Falls and continue east on SR 542. In about 5 miles is a turn-out on the right side with a sign describing the view of Mt. Baker. The location is distinctive because 50-year-old trees now block all views of the mountain. The sign, none-the-less, is well-maintained. Park here and walk back on the road several hundred feet (just around the corner) to an outcrop on the north side of the road. Take care in walking along the roadway, as there is a traffic hazard. 36 Figure 64 (Above) Palm frond imprints in the Chuckanut Formation, at stop 4. These are typical fossils of the early Chuckanut formation.Younger members exhibit fossils of a cooler climate. Stop 4: Rocks of the Chuckanut Formation The rocks here are a siltstone, a common rock type in the Chuckanut Formation. These are deposits from a shallow lake or boggy area on the great Eocene floodplain, where and when these sediments accumulated. These are rocks of the Padden Member, probably dating from something like 45 million years ago. The obvious features here are the imprints of palm fronds, quite vividly preserved in the fine sediments. On inspection, other leaf fossils can be found, including some fern species. These are probably storm debris, a thick mat of fronds piled in a shallow lake or boggy area. After they were deposited they were covered by a layer of mud, preventing them from decaying. While the leaves themselves eventually turned to carbon, they left these distinctive imprints in the fine sediments. The rocks and fossils in the Chuckanut Formation tell us a great deal about the landscape at that time. By analyzing the flora of the time, we find that the region enjoyed a paratropical climate, averaging something like 70 F, and varying no more than 5 degrees year round. This was a lowland coastal rainforest setting, extending well back into what is now Eastern Washington. A large river likely flowed west through the province, draining to the Pacific Ocean. The Chuckanut Formation is the down-stream equivalent of the Swauk Formation, located east of Snoqualmie Pass in the Cle Elum area. Faulting on the Fraser Fault, starting at about 50 Ma, displaced the Chuckanut Formation by about 90 miles to the north. The Swauk and Chuckanut are remarkably thick accumulations, totaling about 5 km of strata. This makes them among the thickest non-marine sedimentary formations in North America. 37 Figure 65 (Above) Leaf imprints in the Chuckanut Formation. These are probably Magnolia species. Figure 66 (Below) Leaf imprints in the Chuckanut Formation These are from a species called Cinnamonium. Figure 67 (Right) Leaf imprints in the Chuckanut Formation These are ferns, indicating a wet, boggy environment. 38 Figure 68 (Above) The Glacier Ranger Station (“Information Center”) at Glacier. This building was built by CCC crews during the 1930’s. Continue east on SR 542 to the town of Glacier. The town of Glacier was originally sited to take advantage of coal deposits in the hills south of town. These are Chucka nut coal deposits, but they have been baked by lavas of Mount Baker, turning them into “hard” (anthracite) coal. As such, they are the only anthracite deposits west of the Mississippi river. In the end, the outcrop was too limited for mining. The town was a major jumping-off point for various gold rushes in the late 1890’s, and was a rail terminus by 1906. It currently has a population of about 90 people, and has the lowest per-capita income of any town in the state. It sits at an elevation of 906 feet. Continue east to the Glacier Ranger Station (“Information Center”) just outside of town. Restrooms, interpretive displays, and a suitable picnic area. Stop 5: Cataclysms on the North Fork (Lunch) Like many communities built around the bases of our local volcanoes, the hamlet of Glacier was built in part on a flat section of valley floor which was created when large-scale mudflows (lahars) swept down from the volcano above thousands of years ago. Mudflows originating anywhere on the steep northern side of the peak ultimately end up flowing into the Glacier Creek valley, flowing into the Nooksack just above the town. This was not a good site location for a community. There is no warning system, and residents would have less than a one- minute notice to flee to higher ground About 2200 years ago, a very large section (about three hundred million cubic meters) of rock on the south side of Church Mountain, just to the north of town, gave way and slid into the valley here. This mega-landslide filled a section of the valley some 12 km (7 mi) long to a depth of up to 100 meters (300 feet) deep in slide debris. The distinctly hummocky terrane of the valley floor reflects the surface of this landslide.Smaller landslides have filled large sections of the valley all the way down to the town Deming, many occurring over the last two thousand years. This is one of the most 39 Figure 69 (Above) Photograph showing the origins and destination of the Church Mountain Landslide. The upper valley is filled by deposits of this event. USGS photo. Figure 70 (Below) Illustration showing route to Stop 7. Base image from Google Earth. seismically-active areas in the region, and is regularly rocked by moderate –scale shallow earthquakes. This activity, along with other factors, contributes to the local mountain-slope failures. Continue east out of Glacier on Highway 542, crossing the Nooksack River and continuing about 5 miles. At a point beyond the turnoff for the Church Mountain Road, about a mile before the turnoff to Excelsior, a short spur road extends off the north side of the highway. Follow this dirt road for about a quarter mile to a fork, and take the right fork into a gravel pit. Stop 7 Glacier 40 Figure 71 (Above) Clam fossils from the Nooksack Group. Taken at stop 6. Most of these are Buccia species. Stop 6: The Nooksack Group This location is a gravel pit dug into a glacial moraine along the valley floor. It is not a particularly scenic setting, a popular site for dumping and target-practice. Moreover, the rocks here are not part of an outcrop, but are glacial “float” – distained by geologists because we can’t be certain of its origins. None the less, the rocks here (the black ones) are typical of this locale – a fact which can be verified by hiking up the road a couple hundred yards to an outcrop. Here, they occur in abundance. These are rocks of the Nooksack Group, a thick (2 km) section of volcanically-derived sandstones and siltstones which accumulated in the shallows around the Chilliwack Islands between 140 and 120 million years ago – just before this terrane belt was accreted to the continental margin. These are part of the larger Gambier Group of volcanic sediments, which are distributed across the southern Insular Belt (See figure 8). The Nooksack Group is the remains of a submarine debris fan which developed around the island volcano. This debris would build up until it avalanched down the slope, burying the surface in a debris flow. In the process, it buried living creatures (here, clams) which became fossilized. As a result, the rocks here contain abundant fossils of clam shells. The two common varieties are Buccia and Pina Clams, the former of which are diagnostic of an Early Cretaceous age. Also present here are the fossilized shells of belemnites, free-swimming squid-type creatures with a conical shell. These are often present as cone-shaped holes in the rocks, some several centimeters in diameter. These creatures all lived, and died, in the waters surrounding the Chilliwack Islands, along the southern end of the Insular Belt Archipelago, in Early Cretaceous time. 41 Figure 72 (Right) Illustration of a belemnite, a cone-shelled mollusc which frequented the Early Cretaceous seas. Its cone-shaped shell fossils are common in the rocks here. Figure 73 (Below) The Nooksack Group, high on the north side of Mt. Baker. The distinctive beds here result from turbidite flows, submarine avalanches which flowed down the debris fan which comprised these sediments. Each bed shows the characteristic fining-upward sequence typical of such flows. 42 Return to Highway 542 and continue to its end at Artists Point, above the Mtl. Baker Ski area. Figures 74, 75, 76, 77 (This page and top right of far page) Columnar andesite exposed on the route up to Austin Pass.These features result as volcanic rock shrinks as it cools. From among the three shapes which can pattern a surface (squares, triangles or hexagons), it selects the shape with the most surface area per volume (hexagons) - the most efficient shape for radiating heat. In general, columns usually extend toward the surface of the flow. Much larger columns can be seen in the Columbia River Basalt Flows of EasternWashington, where they are a common feature. Of note, designers considered using this material to construct the Mt. Baker Lodge in the 1920’s, but instead selected a design of Cedar construction. In the end, the lodge burned down. 43 Figure 77 (Right) The pattern of columnar volcanic rocks. Note how the hexagon shape predominates. From a locale along the Mt. Baker Highway. Figure 78 (Left) A small tarn (glacially-carved pond) below the ski area. The pond is cut into rocks of the Chilliwack Terrane, which underlies the Mt. Baker Volcanics here A popular trail wanders through a number of these ponds during summer time. 44 Stop 7: Austin Pass: Mount Baker, Mt. Shuksan and Glacial Processes The modern cone of Mt. Baker is only the most recent in a long history of volcanic peaks which have erupted in this area over the past couple of million years. Like most volcanoes supported by subduction systems, the volcanic rocks here are largely a variety called andesite. Compared to the thin, runny lavas which characterize basalt, andesite is a thick and chunky mix with a pasty consistency. Because volcanic gasses cannot escape this magma easily, these volcanoes tend to erupt explosively. A 1.1 million year-old explosion caldera on the southeast side of (what is now) Mt. Baker is the remains of an event which blanketed the region in ash, some 30 cm (1 foot) of which are preserved in the bottom of Lake Tapps, southeast of Seattle. Similar explosion calderas extend east from this locale, a legacy of very violent eruptive events. The modern cone of Mt. Baker has probably been constructed largely over the last 50,000 years. It consists almost entirely of andesite flows, with only limited pyroclastic debris. Except on the north side, the peak retains the classic conical form of a stratovolcano. It rises above a pre-existing landscape of about 7500 feet in elevation. It last erupted in 1870, but has a rich history of eruptive events over the past few thousand years. It has indubitably killed many people over the last 5,000 years. The biggest danger from Mt. Baker is the prospect of large volcanic mudflows (lahars) which would result from a significant eruption. Mudflow debris floors most of the major valleys radiating from the peak. Large mudflows on the south side of the peak would sweep into Baker Lake and Lake Shannon below: lakes impounded by old dams of questionable strength. Dam failures would result in a large-scale loss of life in the town of Concrete, and in the towns below on the 45 Figure 78 (Left) Mount Shuksan from Highwood Lake. A classic photographic view. Figure 79 (Above) The Border Peaks range, looking north from the Ski area. Figure 80 (Right) Mount Shuksan and the Austin Pass Road. Figure 81 (Below) Mount Baker, showing the location of the 1.1 Ma Kulshan Caldera, a large explosion feature which pre-dated the modern peak of Mt. Baker. Note light-colored ash deposits in the cliffs. 46 Figure 82 (Above) Mount Baker, from Austin Pass. The active crater (Sherman Crater) is on the left skyline. Owing to its relatively well-preserved state, we susupect that the modern cone was largely accumulated over the last 50,000 years. Figure 83 (Right) Mount Baker from the Austin Pass area. This is a very popular area in the fall, when seasonal colors mark the landscape., Skagit Valley. Mount Shuksan is comprised largely of Shuksan Greenschist and Darrington Phyllite, and is carved from the thick “thrust sheet” of these rocks which overlies the Chilliwack Terrane. At 9127 feet, it is one of the highest non-volcanic peaks in the range, and its form has been extensively sculpted by alpine glaciers. Hanging glaciers on its flanks terminate in ice cliffs, which periodically send boxcar-sized blocks crashing to the valley below. Its name translates to “roaring mountain.” The area around Austin Pass and Heather Meadows strongly reflects the actions of glaciers sculpting the landscape. 47 Figure 84 Mount Shuksan from Austin Pass. This peak is comprised of Shuksan Greenschist and Darrington Phyllite, of the Northwest Cascades Belt. This is a thick thrust-sheet of rock which was driven north over the Chilliwack Terrane, perhaps 90-95 million years ago. Glacial striations (scratches) in rocks at the pass reflect the southward flow of continental-scale ice over the pass from the Nooksack to the Skagit Valleys. The Heather Meadows landscape is carved into glacial cirques, many of which hold small lakes and subalpine tarns, These have resulted from the actions of more local alpine glaciers, and reflect repeated episodes of alpine glaciation. 48 Figure 85 (Right) The Lake Anne plutonic rocks (red area),are the roots of a volcano which grew here several million years ago. Figure 86 (Below) Table Mountain, a good example of “inverted topopgraphy” These are lava flows which accumulated in a valley bottom. Since that time, the sides of the valley have eroded away, leaving this flow perched on a ridge-top. Figures 87, 88 (far page) Views of Mt. Shuksan and Mt. Baker, from Austin Pass. 49 50 A Final Word From Your Instructor: The Pacific Northwest is home to some of the most remarkable geology to be found anywhere on the planet. No region can claim to a greater variety of rock types, or features them in more spectacular settings. More significantly, no region affords such a remarkable venue on the truly collosal forces which drive the dynamics of our planet, or such graphic illustrations on the variety of geologic processes which they support. There is simply no better place on the planet to see how the Earth works. There is certainly no better place on Earth to learn and experience geology. Most students who are taking this course are not planning to major in the sciences, and have other plans for their immediate future. My intention is not to dissuade anyone from following their passions. My only point is that, if you are planning on living in this area (and what rational person wouldn’t?), you should know that you are living in the midst of some of the most incredible geology in the world. You should know that the modern landscape that surrounds you is the product of a truly amazing course of geologic history, one that stretches back hundreds of millions of years. You should recognize that you occupy a unique point in time and space in that course of history, and in the ongoing geologic processes which will continue to shape this region into the future. John 51 This document was prepared for the exclusive use of students enrolled in Geology / Science 111, at North Seattle Community College, to whom it is provided as part of that body of academic coursework. This document should be retained by the student, or destroyed after use. This document should not be made available for purchase in any form, or under any circumstances. By accepting this document, students agree to the conditions for its use, as detailed on this page. Neither the author nor the publisher receive any compensation from the limited distribution of this document.
