Download Geology of Lava Beds National Monument

Geology of
Lava Beds National Monument
Geology 72
William Hirt
Department of Natural Sciences
College of the Siskiyous
800 College Avenue
Weed, California 96094
Hirt—Geology of Lava Beds National Monument
Introduction
This overview of the geology and geologic history
of Lava Beds National Monument (LBNM) has been
written to provide background information for College of the Siskiyous’ Geology of Lava Beds National
Monument short-course (Geology 72), and to serve
as a road log for the course’s field trip. The research
reported here has been drawn from sources cited in
references, especially works by Donnelly-Nolan and
Champion (1987) and Donnelly-Nolan et al. (2007).
Any errors or omissions, however, are solely the responsibility of the author.
Location and Geologic Setting
LBNM is located in the in eastern Siskiyou County just
south of the Oregon border and southwest of the
town of Tulelake (Fig. 1). The monument was established in 1935 to preserve a diverse suite of young
volcanic features on the northern flank of the Medicine Lake Volcano as well as key sites related to the
Modoc Indian War of 1872-1873.
LBNM lies along the boundary between the High Cascade and Basin and Range geologic provinces and displays features characteristic of each. The sections that
follow will describe the monument’s global geologic
setting, the regional extension that defines its basic
crustal structure, and the volcanic processes that have
created its signature landforms.
Figure 1. Map showing the location of Lava Beds National Monument, the caldera atop the Medicine Lake Volcano, and selected
towns and roads (Topinka, USGS/CVO, 1997).
floor volcanoes that lies offshore between Cape Mendocino and Vancouver Island. As the Pacific and Juan
de Fuca Plates move apart, basalt magma generated
by partial melting of the underlying asthenosphere
rises to fill fractures between them and so creates
new oceanic lithosphere at an average rate of a about
1 centimeter per year.
Plate Tectonics
Since the early 1960s geologists have realized that the
distribution of most of the volcanic and seismic activity on Earth can be understood in terms of interactions
between rigid plates of rock that cover the planet’s
surface. These lithospheric plates are 100 to 150 km
thick and consist of the crust and the cold, rigid upper
mantle beneath it. The plates, in turn, lie atop a weaker partially-molten layer of the mantle that extends
to a depth of about 350 km. This weak asthenosphere
permits the plates to move about relatively easily,
and to interact with one another along three types of
boundaries: divergent, convergent, and shear.
The Cascadia Subduction Zone is a fault that dips
eastward beneath the continent and separates the
sinking Juan de Fuca Plate from the overriding North
American Plate. Heating of the subducting oceanic
lithosphere causes it to release water which, in turn,
triggers melting of the overlying asthenosphere. At a
depth of about 100 km enough basalt melt forms that
it is able to separate itself from the surrounding mantle and rise towards the surface. Most of this magma
(melt + entrained crystals) lodges in or near the base
of the crust where it either crystallizes or partially
melts crustal rocks and mixes with them. If mixing
occurs, the resulting andesite magmas may continue
to rise and some of them—perhaps 10%—reach the
Along the western margin of North America these
boundary types are exemplified by the Juan de Fuca
Ridge, Cascadia Subduction Zone, and San Andreas
Fault, respectively (Fig. 2). The ridge is a chain of sea2
Hirt—Geology of Lava Beds National Monument
the western margin of North America for over 100
million years. When a small part of the intervening
Farallon Plate was completely subducted, the North
American and Pacific Plates came into direct contact
and the San Andreas developed as a result of the
shear between them (Fig. 3). It has since grown to a
length of 750 kilometers, and is but one strand in a
broad zone of right-lateral deformation that extends
eastward to the Nevada border.
In southern and central California the Basin and Range
Province lies to the east of this deformation zone.
Although the exact mechanism that links these two
features is unclear, both are apparently manifestations of the strong coupling that now exists between
North America and the adjoining Pacific Plate. Across
the Basin and Range the North American plate is being stretched, and has broken into a series of parallel
mountain and valley blocks separated by north-trending faults. North of Cape Mendocino the San Andreas
Fault ends, but the Basin and Range Province continues through northeastern California and into Oregon.
The Basin and Range Province adjoins the High Cascades near LBNM, and it is at the juncture between
these two provinces that magmas have risen along
north-trending fractures to build the Medicine Lake
Volcano.
Figure 2. Simplified tectonic map of the Pacific Northwest showing the Juan de Fuca Ridge, Cascadia Subduction Zone, and High
Cascade volcanic arc. LBNM lies on the northern flank of the
Medicine Lake Volcano.
surface and erupt to build stratovolcanoes like Mount
Shasta. Because of friction, the upper parts of the
Juan de Fuca and North American Plates are often
“locked” along the Cascadia Subduction Zone. Ongoing plate motion creates strain energy in this locked
region until, every few hundred of years, the rocks
break and the stored energy is released suddenly as
an earthquake. The last major quake along the Cascadia Subduction Zone occurred in January 1700, and
had a magnitude of about 9 (Satake et al., 1996).
In LBNM the effects of regional extension can be seen
in north-trending fault scarps, volcanic lineaments,
and the flat down-dropped floor of the Tule Lake
Basin. Several prominent fault scarps, such as Gillem
Bluff, are exposed near the northwestern margin of
the monument (Fig. 4) and are the results of young
(post 200,000 year) normal faulting. In addition,
volcanic vents such as those at Black Crater and Kings
Rift lie along northerly alignments that suggest similar
fractures exist at depth and have served as conduits
for magmas to reach the surface. Finally, the floor of
the Tule Lake Basin itself is a graben or down-dropped
block between the mountain ranges that flank the
basin.
The San Andreas Fault is a shear boundary that
separates the Pacific and North American Plates. The
part of California that lies west of the fault is moving
northwestward relative to the rest of the continent
at an average rate of about 3 centimeters per year. As
with the Cascadia Subduction Zone, parts of the San
Andreas Fault are often locked so that strain energy
accumulates for decades or centuries before the rocks
break and release suddenly as an earthquake.
Back Arc Volcanism
Although the chemistry of its lavas suggest that the
Medicine Lake Volcano is related to the High Cascades, its location on the eastern side of the arc and
its eruption of mostly basalt rather than andesite
lavas indicate it is not a typical subduction zone vol-
Basin and Range Extension
The San Andreas Fault did not exist prior to about
27 Ma. It was formed when one part of the Farallon
Ridge reached the subduction zone that had marked
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Hirt—Geology of Lava Beds National Monument
Figure 4. Gillem Bluff is a scarp along which basalt lava flows at
least 2 million years old have been uplifted on the western (left)
side of a normal fault.
masses that cannot mix with the rhyolites and the
volcano erupts a bimodal assemblage of rhyolite and
basalt (Fig. 6). Beneath Mount Shasta, on the other
hand, “wet” basalt magmas remain molten to lower
temperatures and so are able to mix with crustal
rhyolites to produce lavas of intermediate composition. Although we will not see any of the rhyolitic
lavas erupted from the Medicine Lake Volcano “in
place” during our field trip, keep your eyes peeled for
fragments of white rhyolite pumice that were scattered across the monument during the eruption of
Glass Mountain 900 years ago.
Volcanic rocks and their eruptive characters
The eruptive behavior of lavas is strongly influenced
by their temperatures, compositions, and volatile
contents. Silicon and oxygen are the most abundant
elements in Earth’s crust and mantle, and together
they comprise about 50 to 70 weight percent of most
volcanic rocks. Silicon-oxygen groups link strongly
together, and if they are abundant in a melt they tend
to make it very viscous (“pasty”). In fact, variations
in viscosity account for three of the main differences
between silica-rich (rhyolite) and silica-poor (basalt)
lavas. First, because it is difficult for crystals to grow
in viscous melts, cooling rhyolite lava often quenches
to glass (obsidian) instead of forming crystalline rock.
Second, because it is difficult for gases to escape from
viscous melts, rhyolite lava typically erupts more explosively than basalt lava. The white rhyolite pumice
scattered across the monument is clearly full of gas
bubbles, and was blown here by eruptions that oc-
Figure 3. Simplified block diagrams showing the development of
the San Andreas Fault. (USGS Western Earth Surface Processes
Team).
cano. Along with the Newberry Volcano farther north,
Medicine Lake is one of two “back arc” volcanoes in
the Oregon Cascades. The relatively “dry” (waterpoor) basalt lavas it produces originate from upwelling of hot asthenosphere that circulates above the
sinking Juan de Fuca Plate rather than from melting
triggered by the volatiles the plate releases (Fig. 5).
Basalts that rise beneath both the main and back-arc
parts of the southern Cascades heat the surrounding
continental crust and produce relatively cool rhyolite
magmas. Because the Medicine Lake Volcano’s basalts
are so water-poor, however, they solidify at higher
temperatures than do the water-rich basalts produced
farther west. As a result, when Medicine Lake basalts
encounter crustal magmas they chill to semisolid
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Hirt—Geology of Lava Beds National Monument
Figure 5. Schematic cross-section of the Cascade arc at the
latitude of LBNM. Note that magmas (stars) form just above the
sinking plate (“slab”) under Mount Shasta and at a much shallower depth beneath the Medicine Lake Volcano due to mantle
upwelling. After Elkins-Tanton et al. (2001).
curred at Glass Mountain 25 kilometers to the south.
Finally, it is difficult for viscous lava to flow downhill, so rhyolite lavas tend to build thick, steep-sided
domes atop their vents rather than forming long thin
flows as basalt lavas do.
Figure 6. Simplified geologic map of the Medicine Lake volcano
showing post-glacial volcanic vents and the extents of basalt and
rhyolite flows. From Donnelly-Nolan et al. (2007).
Volcanic Features
Medicine Lake Shield Volcano
The landscape of LBNM is dominated by basalt lava
flows and tephra cones that erupted from fissures
on the northern flank of the Medicine Lake volcano.
This large shield volcano dominates the monument’s
southern skyline (Fig. 7) and has been active for about
500,000 years (Donnelly-Nolan et al., 2007). Since
the end of Pleistocene glaciations about 12,500 years
ago the Medicine Lake volcano has produced sixteen
eruptions of rhyolite and basalt (Fig. 6). The volume of
the basalts erupted during this period has been about
four times that of the rhyolites.
nated from its summit or from fissures farther down
its slopes. A small, partially buried caldera dominates the mountain’s summit, and was formed about
180,000 years ago during the eruption of the Tuff of
Anderson Well. This ash-flow tuff is widely distributed
across the northern side of the volcano and can be
seen in low outcrops just west of LBMN.
Lava Flows and Lava Tubes
Although at least thirty separate lava flows crop out
within the boundaries of LBNM just one, the Basalt of Mammoth Crater, covers nearly 70% of the
monument’s area (Donnelly-Nolan et al., 2007). Most
of these flows are basalts, but smaller amounts of
slightly more silica-rich basaltic andesite and andesite
also occur. The surface textures of the flows depend
The volcano’s broad profile indicates it has been built
by hundreds relatively thin basalt lava flows that origi5
Hirt—Geology of Lava Beds National Monument
Figure 7. Photograph of the Medicine Lake volcano looking south. Note the low broad profile typical of a shield volcano and the small
tephra cones dotting its surface.
on the viscosities of the lavas which, in turn, depend
on their temperatures and volatile concentrations as
well as their silica contents. Smooth “ropy” surfaces
develop as a soft flexible “skin” formed on top of the
flows is folded if they stop moving while they are still
hot and fluid. Rough “blocky” surfaces develop, on
the other hand, where a thicker crust is formed and
repeatedly broken as a flow continues to move even
when it is cool and viscous. These surface textures will
commonly change from ropy to blocky as lava moves
away from its source, cools, and loses volatiles. For example, compare the texture of the Devil’s Homestead
Andesite at the overlook (far from its source) with its
texture at Fleener Chimneys (near its source).
Some lava tubes in the monument also contain perennial ice which forms where water seeping down from
the surface encounters cold air that seasonally collects in the lower parts of the tube systems.
Pit Craters
Mammoth Crater, the vent for the largest lava flow in
the monument, is not a crater at all in the traditional
sense. Rather than having been excavated by explosive eruptions, this steep-walled circular “pit” was
formed by subsidence above a shallow magma reservoir whose contents drained out elsewhere down
slope.
Tephra Cones
Volatiles dissolved in magma will escape as it reaches
the surface, and if their escape is sufficiently violent
they will tear the magma apart and throw the fragments through the air as tephra. This material consists
of fine ash, pea-sized lapilli, and larger blocks (angular) and bombs (rounded). Tephra cones, like Schonchin Butte, are small round hills built by the accumulation of this material around a vent. Their flanks are
typically loose and steep, and their vents are marked
by circular craters. Although fresh basaltic tephra is
black, the oxidation of iron in the hot tephra by air or
volcanic gases commonly gives cinder cones a reddish
color.
Like most liquids, lavas shrink as they cool and solidify.
After a flow has come to rest, it will cool inwards
from its top and bottom surfaces. Shrinkage fractures
develop perpendicular to these cooling surfaces and
grow inward as the flow cools. These fractures split
the cooling lava into polygonal columns. Look for
these columnar joints in the lavas exposed near the
entrance to Skull Cave.
LBNM is well-known for its lava tubes, and at least
436 of these “caves” are found throughout the monument. Unlike true caves, lava tubes are formed as
the fluid centers of lava flows drain away after their
outer parts have solidified. Some are “surface tubes”
formed from small flow lobes, whereas other larger
ones are formed by the “roofing over” of lava-filled
channels. Many of the monument’s large lava tubes
occur in the Basalt of Mammoth Crater and can be accessed from the Cave Loop Road just southwest of the
visitor center. Mushpot Cave, which has a paved trail
and explanatory displays, is part of this tube system.
Spatter Cones
If the escape of volatiles from magma is not vigorous enough to fragment it into tephra, it will instead
throw small soft masses of lava out of the vent to
form spatter. Such masses only travel short distances
through the air and are still hot and semi-solid when
they land next to the vent. They will pile up there
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Hirt—Geology of Lava Beds National Monument
and typically partially fuse back together to form a
spatter cone. Chains of these small cones commonly
develop along the length of an erupting fissure during
the early stages of an eruption, as at Ross Chimneys.
As the eruption proceeds parts of the fissure typically become blocked and only a few of the cones
remain active as the volatiles are exhausted and the
“fire fountaining” phase of the eruption ends. Fleener
Chimneys, at the head of the Devil’s Homestead flow,
are excellent examples of spatter cones.
Glass Mountain Rhyolite
885 years
Field Trip Road Log
LBNM northern boundary: road log begins. Note that
it is illegal to disturb or collect any rocks, plants, or
animals in the monument.
STOP 1. Gillem Bluff: Basalt lava flows more than
2,000,000 years old are exposed in this cliff after
having been uplifted on the western side of a normal
fault that bounds the Tule Lake basin. This northtrending fault is typical of those that accommodate
Basin and Range extension in this area.
Tuff Cones and Tule Lake
In the far northeastern corner of LBNM there are two
well-preserved tuff cones that were built by explosive eruptions triggered when basalt lavas came into
contact with the water in Tule Lake. Prisoners Rock
and The Peninsula were formed about 275,000 years
ago when…
STOP 2. Devil’s Homestead Flow: From this overlook
you can see the surface texture of the distal part of
the 10,500-year old Devil’s Homestead andesite flow.
By the time it reached this location the lava was relatively cool and volatile-poor, and so developed this
blocky (aa) texture. [619571 E, 4627602 N, 4214 ft.]
Geologic History Summary
Below is a list of the estimated ages of some of the
major eruptive events that have produced the features we’ll see in LBNM. Most of the dates are taken
from a NPS handout prepared by Donnelly-Nolan
(2000).
STOP 3. Fleener Chimneys spatter cones: These spatter cones formed at the vent of the Devil’s Homestead
andesite flow. Notice the local development of ropy
(pahoehoe) texture here where the lava was hot and
volatile rich. Also notice the small surface tube on
the right side of the trail as you walk up towards the
cones from the parking lot. [619172 E, 4623623 N,
4455 ft.]
Gillem Bluff lavas
> 2,000,000 years
Medicine Lake volcano (entire history)
500,000 years
Basalt of Hovey Point
450,000 years
Prisoners Rock and The Peninsula
275,000 years
Tuff of Anderson Well
180,000 years
Schonchin Butte Andesite
62,000 years
Mammoth Crater and Modoc Crater
30,000-40,000 years
Fleener Chimneys, Devils Homestead Basalt
10,500 years
Basalt of Black Crater
3,025 years
Cinder Butte, Callahan Basaltic Andesite
1,110 years
Little Glass Mountain Rhyolite
1,065 years
STOP 3. Schonchin Butte tephra cone: This tephra
cone and its associated lava flow formed about
62,000 years ago. A hike up to the old lookout tower
on top will be rewarded with panoramic views of the
monument, the Medicine Lake volcano to the south,
Mount Shasta to the west, and the cone’s small summit crater. [622723 E, 4621854 N, 4806 ft.]
STOP 4. LBNM Headquarters and Mushpot Cave: The
visitors center has displays describing both the volcanic and human history of the monument. Be sure
to look at the scale models of Mount Shasta and the
Medicine Lake volcano to get a sense of the differences in size and shape between a stratovolcano and
a shield volcano. Also, take the short hike south from
the visitors center to Mushpot Cave and tour the well7
Hirt—Geology of Lava Beds National Monument
signed interior of this short but geologically diverse
lava tube. [624075 E, 4618940 N, 4760 ft.]
plagioclase.
Basaltic andesite: A volcanic rock that contains between 52 and 57 weight percent silica. Basaltic andesites are typically black in color and contain visible
crystals of plagioclase, olivine, and augite.
STOP 5: Mammoth Crater: This pit crater, which was
active 30,000 to 40,000 years ago, is the source of the
basalt that covers over 70% of the monument. Just
across the road from the crater a short trail leads to
Hidden Valley, a very large lava tube whose roof has
collapsed. [621043 E, 4616559 N, 5538 ft.]
Crystal: A piece of solid material within which all of
the atoms are arranged in a regular, three-dimensional pattern. Some crystals have smooth external
surfaces (faces) that formed as they grew from a melt
or vapor.
STOP 6: Skull Cave: This large lava tube was a major
feeder channel for the Basalt of Modoc Crater and
was formed 30,000-40,000 years old. It is named for
a collection of human and animal bones that were
found in the pit at the eastern end of the main chamber. A trail leads from the entrance to the top of the
pit, and a metal staircase takes you to a lower level
with a floor of permanent ice. [623945 E, 4020797N,
4548 ft.]
Dacite: A volcanic rock that contains between 63 and
72 weight percent silica. Dacites are typically gray
to pink in color and contain visible crystals of plagioclase, hypersthene, and hornblende.
Debris avalanche: A dense, incoherent mixture of
water, rock, and soil that flows down slope at speeds
of 40 to 200 km/hr (25 to 125 mi/hr).
STOP 7: Petroglyph Point and Prisoner’s Rock tuff
cone: This tuff cone was formed about 275,000 years
ago by hydrovolcanic activity in Tule Lake. The lake
has since been diked and drained, but the wave cut
terrace adjacent to the parking area and the petroglyphs cut into the side of the cliff just above the old
waterline give you an idea of how deep it used to
be. To the north is The Peninsula, another tuff cone
of similar age that once contained a basalt lava lake.
[633670 E, 4633666 N, 4069 ft.]
Debris flow: A dense, incoherent mixture of water,
rock, and soil that flows down slope at speed of 2 to
40 km/hr (1 to 25 mi/hr).
Dike: A sheet-like body of solidified magma that cuts
across layering or other structures in the surrounding
rock.
Dome: A relatively small, steep-sided volcano formed
by pasty lava that has piled up atop its vent. Domes
are typically no larger than 2 to 3 km (1 to 2 mi) in
diameter and are composed of silica-rich lavas.
Glossary
Andesite: A volcanic rock that contains between 56
and 63 weight percent silica. Andesites are typically
gray or black in color and contain visible crystals of
plagioclase, augite, and hypersthene.
Holocene Epoch: The period of time from 10,000
years ago to present. On Earth this corresponds to
the time since the last retreat of widespread continental glaciers.
Asthenosphere: Part of the Earth’s mantle that lies
below the lithosphere, at depths between about 100
and 350 kilometers. Rock here is relatively soft because its high temperature and relatively low confining pressure enable a small amount of melt to form
and lubricate its movement.
Lava: Partially molten rock that has risen through
Earth’s crust and been erupted onto the surface.
Magma: partially molten rock that consists of melt
with or without entrained crystals and vapor bubbles.
Basalt: A volcanic rock that contains between 47 and
52 weight percent silica. Basalts are typically black
and commonly contain visible crystals of olivine and
Mineral: A solid natural material that has a specific
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Hirt—Geology of Lava Beds National Monument
chemical composition and a unique internal arrangement of its atoms. For example, quartz consists of silicon and oxygen atoms in a 1:2 ratio (SiO2), and these
atoms are bonded together in a hexagonal structure.
about 60,000 years old.
Recurrence interval: The average period of time
between two episodic events such as earthquakes,
floods or volcanic eruptions.
Mudflow: A dense suspension of fine rock fragments
in water. A mudflow is a type of debris flow in which
most of the sediment particles are sand-sized (2 mm
across) or smaller.
Rockfall: A moving mass of rock fragments that has
broken loose from an outcrop and cascaded down a
slope.
Peridotite: A dense, coarse-grained rock that consists
mostly of the magnesium and iron-silicate mineral
olivine (”peridot”).
Shield volcano: A broad volcano built of many thin,
overlapping flows of basalt or basaltic andesite lava.
Shield volcanoes differ widely in size, from several
kilometers to several hundreds of kilometers in diameter and have very gently sloping flanks.
Phenocryst: A relatively large crystal in a volcanic rock
that grew from the surrounding melt at depth.
Silicate: A compound formed of silicon and oxygen
with or without other elements. Silicate minerals and
the rocks they are part of make up most of Earth’s
mantle and crust.
Pleistocene Epoch: The period of time between 1.8
million and 10,000 years ago. On Earth this corresponds to the interval during which large continental
glaciers repeatedly advanced and retreated across
landmasses at high latitudes. Informally, this epoch is
also called the “ice age”.
Stratovolcano: A volcano composed of alternating
lava flows, layers of pyroclastic material, and debris
flow deposits piled up around a central vent. Stratovolcanoes are typically 10 to 30 km (6 to 20 mi)
in diameter and have slopes that steepen gradually
upwards towards their summits.
Potassium-argon dating: A technique for determining the age of rock and mineral samples by measuring
the amounts of radioactive potassium (40K) and its
daughter element, a form of argon (40Ar). Because
40K decays relatively slowly, this technique usually
only yields reliable ages for samples that are more
than about 100,000 years old.
Subduction: Process in which a plate of dense oceanic
lithosphere sinks back into Earth’s interior along a
dipping surface that separates it from the overriding
lithosphere and asthenosphere.
Pumice: A porous, glassy volcanic rock formed by
the rapid expansion of gas bubbles in melt that is
quenched as it is erupted.
Subduction zone: A dipping surface that separates a
sinking plate of oceanic lithosphere from the overriding lithosphere and asthenosphere.
Pyroclastic material: Volcanic rock that has been
fragmented by explosions during an eruption or by
the collapse and disintegration of the flanks of domes
or lava flows.
Tephra: Fragmental volcanic rock formed by lava that
has been blown explosively from a vent and solidified
as it traveled through the air.
Radiocarbon dating: A technique for determining the
age of a sample of organic material (charred wood,
plant roots, cloth) by measuring the rate at which the
radioactive carbon (14C) it contains is decaying. Because 14C decays relatively rapidly, this technique only
yields accurate ages for samples that are less than
Tephra cone: A volcano composed of layers of tephra
piled up around a central vent or crater. Tephra cones
are typically 1 to 2 km (1 mile) in diameter and have
steep (35 to 40o) slopes determined by the angle at
which the loose tephra begins to slide.
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Hirt—Geology of Lava Beds National Monument
Texture: Description of how the various materials that
make up a rock (crystals, glass, and fragments of other
rocks) are arranged with respect to one another.
Tuff: A rock made of fine volcanic tephra that has
been cemented or partially fused (welded) together.
147-163.
Satake, K., Shimazaki, K., Tsuji, Y., and Ueda, K., 1996,
Time and size of a giant earthquake in Cascadia
inferred from Japanese tsunami records of January
1700: Nature, v. 379, p. 246-248.
Tuff breccia: A rock made of tephra and other pyroclastic materials of a wide range of sizes that have
been cemented or partially fused together. Large
fragments are angular.
Volatiles: Chemical compounds and elements (such
as water, H2O, and nitrogen, N2) that occur as gases at
high temperatures and atmospheric pressure.
Volcanic arc: A chain of volcanic peaks that stands
above a subduction zone. Because Earth’s surface is
spherical, subduction zones and the chains of volcanoes that develop above them are inevitably curved.
Volcaniclastic material: Fragmented volcanic rock
deposited by either pyroclastic or debris flows.
References
Donnelly-Nolan, J.M., and Champion, D.E., 1987,
Geologic map of Lava Beds National Monument: U.S.
Geological Survey Map I-1804, scale 1:24,000.
Donnelly-Nolan, J.M., Nathenson, M., Champion, D.E.,
Ramsey, D. W. , Lowenstern, J. B., and Ewert, J.W.,
2007, Volcano hazards assessment for Medicine Lake
Volcano, Northern California, U.S. Geological Survey
Scientific Investigations Report 2007-5174-A, 26 p.
Elkins Tanton, L.T., Grove, T.L., and Donnelly-Nolan, J.,
2001, Hot, shallow melting under the Cascades volcanic arc: Geology, v. 29, no. 7, p. 631-634.
Lavine, A., 1994, Geology of Prisoners Rock and The
Peninsula: Pleistocene hydrovolcanism in the Tule
Lake basin, northeastern California: California Geology, v. 47, no. 4, p. 95-103.
Lavine, A., and Aalto, K.R., 2002, Morphology of a
crater-filling lava lake margin, The Peninsula tuff cone,
Tule Lake National Wildlife Refuge, California: implications for the formation of peperite textures: Journal
of Volcanology and Geothermal Research, v. 114, p.
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