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Physical Geography: Landforms of California Overview • • • • • • Geologic Time Movements of the Continents Earth Materials Tectonic Forces Weathering and Erosion Processes Erosional Agents and Deposition Geologic Time Pretend the age of the earth (4.6+ billion years) is compressed into one calendar year. January 1 - Earth and planets formed Early March - liquid water stands in pools. Late March - earliest life July - oxygen is important part of atmosphere October 25 - multicellular organisms Late November - plants and animals abundant December 15 to 25 - dinosaurs arise and disappear 11:20 pm, December 31 - Humans appear One second before midnight - Automobile invented The Earth’s Interior • General trends: temperature, density • Horizon composition, behavior Distance: 6730 km (3963 miles) Earth Materials • Three major rock types – Igneous – Sedimentary – Metamorphic Igneous Rocks • Igneous (ignus = fire) • Formed from the cooling of molten rock (magma/lava), a process called crystallization. – Slow cooling larger crystals > dense rock – Rapid cooling small crystals > lighter rock • Two classes of igneous rocks – intrusive: formed inside the Earth – extrusive: formed at Earth’s surface Igneous Intrusive Rocks • Cools slowly (thousands of years) • Visible crystals • Examples - granite - diorite - gabbro Igneous Extrusive Rocks • Cools rapidly - exposed to surface • No visible crystals • Examples - rhyolite - andesite -basalt Typical Igneous Intrusions Know: Batholith and Dike Exposed Batholiths Sierra Nevada, CA Sedimentary Rocks Sedimentary Rocks Relative Abundance by Type Compaction Cementing Formation Limestone (CaCO3) Shale (fine grains) Sandstone (larger grains) Where do Sedimentary Rocks Form? Terrestrial environments (non-marine) Marine environments Continental shelf Rivers and floodplains (fluvial environment) Continental slope and rise (deep sea fans) Lakes Abyssal plain Deserts (aeolian environment) Beach and barrier islands Metamorphic Rocks or That’s very Gneiss, but I don’t give a Schist! Schist (narrow foliation) Gneiss (broad foliation) The Unstable Landscape: California Plate Tectonics • Crustal Processes – Destruction (subduction) – Creation (volcanism ) – Alteration / deformation (folding and faulting) Introduction • Plate boundaries: main location for Earth’s volcanic and earthquake activity. • Type of plate boundary determines activity. • 3 types – diverging (spreading) – converging (colliding) – transform (sliding past each other) Convergent Plate Boundaries • Action: – collision; destructional or constructional • Activity: – depends on type of convergence – 3 types: ocean-continent, ocean-ocean, cont.-cont. Convergent: Ocean-continent • Action: – collision; destructional (subduction of ocean plate) • Activity: – shallow to deep earthquakes; volcanism (continental) • Features: – ocean trench; volcanic mtns on continental margin Volcanoes: Explosive • Composite cones (stratovolcano) – pointed, steep-sided, tall volcanoes – “Composite”: layers of pyroclastics and lava (mostly felsic) – Explosive and dangerous; found near subduction zones Volcanoes: Explosive Arenal, Costa Rica Mt. Shasta, California Mt. Lassen, California Crustal Deformation: Folding, Faulting, and Earthquakes Introduction • Crustal Processes – Destruction (subduction) – Creation (volcanism - convergent/divergent) – Alteration / deformation (folding and faulting) Crustal Deformation • Outcome / result of “battle”: Stress v. strain (force v. resistance) – Stress: force imposed on the rock (tension, compression and shear) – Strain: how the rock responds to the stress (folding / bending or faulting / breaking) Is the rock brittle or ductile? Figure 12-7 Faulting • Definition: fractures where some type of displacement (movement) has occurred along a break in rock. • Three types – normal – reverse/thrust – transform (strike-slip) Carmel Valley Fault, CA Normal Faults • Tensional stress • Earthquake and displacement along fault plane fault scarp Landforms - Normal Faulting Owens Valley, CA Sierra Nevada, CA Grand Tetons, WY Basin and Range • Horst and graben (“hill” and “grave”) Death Valley/ Panamint Ranges Why saline? Landforms: Normal Faulting • Grabens (“Graves”) Basin and Range Transform Plate Boundary • Action: – shear (lateral motion) – no loss/gain of plate material San Andreas fault system – How long is it? About 1000 km – Relative motion of the Pacific Plate? @ 2 inches (5 cm) northwest per year. In 10 million years Los Angeles will be off of San Francisco . San Andreas Fault System Southern California Transform Plate Boundary • Activity: – shallow to moderate earthquakes – little to no volcanism Tremblor Range Dragon’s Back Carrizo Plain, CA (view to the east) http://quake.usgs.gov/recenteqs/ Transform Plate Boundary • Features: – shallow, linear rift valleys – sag ponds Carrizo Plain, central CA San Andreas Lake (Crystal Springs Reservoir) - looking south along fault - San Francisco water supply - geology vegetation Transform Plate Boundary • Features: – offset streams, objects Stream channel offset, Carrizo Plain, central CA 1906 earthquake offset, Point Reyes, CA The Geography of Earthquakes • USA: 1977-1997 earthquake events • USA: every state except ND, FL The Geography of Earthquakes • Globally: primarily at plate boundaries • Intraplate earthquakes do occur! Mag 6.5 Earthquakes • Earthquakes are the shaking or vibration of the ground as a result of rocks suddenly breaking along a fault. • Focus (hypocenter) = rupture point • Epicenter = point on surface above focus • Foreshocks • Aftershocks Process: the earthquake cycle (elastic rebound theory) • Earthquakes are a ‘release of energy’ in the form of a seismic wave (vibrates the crust). • Plate movement strain builds rocks “locked together” (frictional bond) • Rocks bend hit limit --> rupture/break • Cycle repeats ”start-stop” motion along fault Seismic waves • Some of the waves that are generated by an earthquake travel within the earth and other travel along the surface, creating surface waves. • Waves traveling within the earth are known as body waves. Surface Waves • Surface waves cause the most damage to buildings during an earthquake. • Surface waves can set up liquefaction in wet alluvium. This is where the most extensive damage to buildings occurs. – Liquefaction: wavelike, almost liquid, rolling of surface – Alluvium: fine material deposited by water over many years. Measuring Earthquakes • seismograph: records the vibrations of the crust • Richter Scale measures vibration, not damage. • seismogram: tracing record Major California Earthquakes • Fort Tejon, 1857 - 8.0 magnitude • San Francisco, 1906 - 7.9 magnitude • 1933 Long Beach - 6.3 magnitude Destroyed Glendale College Buildings! • San Fernando, 1971 - 6.6 • Northridge, 1994 - 6.7 • Hector Mine, 1999 - 7.1 • TIME: January 9, 1857 Fort Tejon, 1857 • LOCATION: 35° 43' N, 120° 19' W • about 72 km (45 miles) northeast of San Luis Obispo about 120 km (75 miles) northwest of Bakersfield, as shown on the map (epicenter location uncertain). • MAGNITUDE: Mw 8.3 (approx.) • TYPE OF FAULTING: right-lateral strike-slip • FAULT RUPTURED: San Andreas fault • LENGTH OF SURFACE RUPTURE: about 360 km (225 miles) • MAXIMUM SURFACE OFFSET: about 9 meters (30 feet) San Francisco Aftermath, 1906 Magnitude: 7.9 San Francisco, 1906 Magnitude: 7.9