California Geology

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Information about California Geology

Published on March 20, 2008

Author: Marcell


Slide1:  Physical Geography: Landforms of California Overview:  Overview Geologic Time Movements of the Continents Earth Materials Tectonic Forces Weathering and Erosion Processes Erosional Agents and Deposition Geologic Time:  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 The Earth’s Interior Distance: 6730 km (3963 miles) Earth Materials:  Earth Materials Three major rock types Igneous Sedimentary Metamorphic Igneous Rocks:  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 Slide9:  Two classes of igneous rocks intrusive: formed inside the Earth extrusive: formed at Earth’s surface Igneous Intrusive Rocks:  Igneous Intrusive Rocks Cools slowly (thousands of years) Visible crystals Examples - granite - diorite - gabbro Igneous Extrusive Rocks:  Igneous Extrusive Rocks Cools rapidly - exposed to surface No visible crystals Examples - rhyolite - andesite -basalt Slide12:  Typical Igneous Intrusions Know: Batholith and Dike Exposed Batholiths:  Exposed Batholiths Sierra Nevada, CA Sedimentary Rocks:  Sedimentary Rocks Slide15:  Compaction Cementing Sedimentary Rocks Formation Relative Abundance by Type Slide16:  Sandstone (larger grains) Shale (fine grains) Limestone (CaCO3) Where do Sedimentary Rocks Form?:  Where do Sedimentary Rocks Form? Terrestrial environments (non-marine) Rivers and floodplains (fluvial environment) Lakes Deserts (aeolian environment) Marine environments Continental shelf Continental slope and rise (deep sea fans) Abyssal plain Beach and barrier islands Metamorphic Rocks or That’s very Gneiss, but I don’t give a Schist!:  Metamorphic Rocks or That’s very Gneiss, but I don’t give a Schist! Gneiss (broad foliation) Schist (narrow foliation) The Unstable Landscape: California Plate Tectonics:  The Unstable Landscape: California Plate Tectonics Slide21:  Crustal Processes Destruction (subduction) Creation (volcanism ) Alteration / deformation (folding and faulting) Introduction:  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:  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:  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:  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:  Volcanoes: Explosive Arenal, Costa Rica Mt. Shasta, California Mt. Lassen, California Crustal Deformation: Folding, Faulting, and Earthquakes:  Crustal Deformation: Folding, Faulting, and Earthquakes Introduction:  Introduction Crustal Processes Destruction (subduction) Creation (volcanism - convergent/divergent) Alteration / deformation (folding and faulting) Crustal Deformation:  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? Slide33:  Figure 12-7 Faulting:  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:  Normal Faults Tensional stress Earthquake and displacement along fault plane  fault scarp Landforms - Normal Faulting:  Landforms - Normal Faulting Owens Valley, CA Sierra Nevada, CA Grand Tetons, WY Basin and Range:  Basin and Range Horst and graben (“hill” and “grave”) Death Valley/ Panamint Ranges Why saline? Landforms: Normal Faulting:  Landforms: Normal Faulting Grabens (“Graves”) Basin and Range:  Basin and Range Transform Plate Boundary:  Transform Plate Boundary Action: shear (lateral motion) no loss/gain of plate material Slide42:  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:  San Andreas Fault System - Southern California Transform Plate Boundary:  Transform Plate Boundary Activity: shallow to moderate earthquakes little to no volcanism Tremblor Range Dragon’s Back Carrizo Plain, CA (view to the east) Transform Plate Boundary:  Transform Plate Boundary Features: shallow, linear rift valleys sag ponds San Andreas Lake (Crystal Springs Reservoir) - looking south along fault - San Francisco water supply - geology  vegetation Carrizo Plain, central CA Transform Plate Boundary:  Transform Plate Boundary Features: offset streams, objects Stream channel offset, Carrizo Plain, central CA 1906 earthquake offset, Point Reyes, CA The Geography of Earthquakes:  The Geography of Earthquakes USA: 1977-1997 earthquake events USA: every state except ND, FL The Geography of Earthquakes:  The Geography of Earthquakes Globally: primarily at plate boundaries Intraplate earthquakes do occur! Mag 6.5 Earthquakes:  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):  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:  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 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:  Measuring Earthquakes seismograph: records the vibrations of the crust Richter Scale measures vibration, not damage. seismogram: tracing record Major California Earthquakes:  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 Fort Tejon, 1857:  Fort Tejon, 1857 TIME: January 9, 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) Slide58:  San Francisco Aftermath, 1906 Magnitude: 7.9 San Francisco, 1906 Magnitude: 7.9 :  San Francisco, 1906 Magnitude: 7.9

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