Geologic Overview of Southern California Coastal Areas Continental Margin Coastal & Offshore Faulting Geology of Offshore Islands Orange County Coastal Geology Sediment & Sedimentary Rock Long Shore Currents and Coastal Cells Depositional vs. Erosional Coastlines Geology of San Onofre Landslide and tsunami hazards Mark Bordelon Irvine Valley College Geology of Dana Point area March 2012 Subduction of the Farallon Plate 100 m.y. ago Continental Margins Where land meets the ocean Margins near plate boundaries are ―active.‖ Fig. 3.11 Margins far from plate boundaries are ―passive.‖ Physiographic Provinces of S. Calif. http://scamp.wr.usgs.gov/scgeo Rotation of Transverse Ranges Fritsche and Behl, 2008 Extension creates basins 20-30 m.y. ago Up block Up block Basin Offshore Faulting Newport-Inglewood Fault Zone Huntington Beach Oil Field (1920s) Offshore Islands – N. Channel Islands Four northern Channel Islands are an extension of the Santa Monica Mts. • San Miguel, Santa Rosa, Santa Cruz & Anacapa Islands • Geology consists of Miocene volcanic rocks: pillow basalts, lava flows, tuff • Islands were isolated from one another 12-10 y.b.p. when sea level rose Pygmy Mammoth on Santa Rosa Island Radiocarbon date = 13,000 years old Lower sea level created one large island, 5 miles from mainland Isolated when sea level rose 12,000 y.b.p. http://www.nps.gov/chis/pygmy.htm Channel Islands National Marine Sanctuary http://www.cinms.nos.noaa.gov/ Offshore Islands – S. Channel Islands • Southern islands include Catalina, San Clemente, Santa Barbara and San Nicolas Islands • Remnants of up-faulted blocks • Marine Terraces well-developed on San Clemente Island Marine Terraces – San Clemente Island 25 terraces 2.8 m.y. oldest 580 m high Catalina Island • Catalina Island has extensive outcrops of Catalina Schist on northern portion of island • Represents blueschist metamorphism which is typical of subduction zones. Subduction Metamorphism Subduction creates the unique blueschist facies. A low geothermal gradient—low T, high P. Blueschist minerals Glaucophane Lawsonite Lawsonite Blueschist Geologic Time Scale OC Coastal Geology represented by Neogene sedimentary and igneous rocks Geologic Map of Orange County Sediment vs. Sedimentary Rock Drilling into the bottom of a coastal area, we encounter: Soft mud and loose sand, silt, pebbles, and shells. Then: Similar materials that are more solidified. Then: Fragments of solid rock. Cemented sand and silt. Cemented shells. Transition from loose sediment into cemented sedimentary rock. This change occurs as burial depth increases. Classes of Sedimentary Rock Clastic—loose rock fragments (clasts) cemented together. Biochemical—cemented shells of organisms. Chemical—minerals that crystallize directly from water. Chemical Clasti Biochemica c l Beach • Active Zone of sediment transportation • Beach lies between: • Erosional area above water level • Depositional area below water level Coastal Zones Waves Erode platform Summer vs. Winter Beach Profile Sand Budgets • Estimates of sand gains (inputs) and losses (outputs) to a beach • Beach profile studies • Inputs: • Rivers (Los Angeles, San Gabriel, Santa Ana) • Cliff erosion • Onshore transport of sediment by LSC • Outputs: • Offshore transport of sediment by LSC • Submarine Canyons Newport Beach Harbor Where does the sand go? Longshore Drift Longshore Current and Beach Drift View from Huntington Beach to the south Oblique View of Submarine Canyons Oblique View of Newport Submarine Canyon Coastal Cells in S. Calif. 5 major coastal cells within 200 miles Coastal Cell Model Depositional vs. Erosional Coasts • Depositional Coasts • Rate of accumulation exceeds erosion • LSC slowed, sand deposits • Features: spits, deltas, barrier islands • Erosional Coasts • Strong wave activity; erosion rates high • Rate of erosion depends on • Local geology • Degree of wave exposure • Tidal range • Features: Cliffs, sea stacks, wave-cut platforms Erosional Shoreline Features (Exposure to wave energy high; no slowing of LSC) Sea Arches Sea Stacks- isolated rock remnants Marine Terraces Elevated wave-cut platforms Wave-cut Platforms Emergent & Submergent Coasts Emergent Coastlines Result from uplift and/or sea level drop Features: marine terraces Submergent Coastlines Result from downdrop and/or sea level rise Features: estuaries Geologic Map of San Onofre Area Cristianitos Fault at San Onofre Stratigraphic Cross-Section at SONGS Area Onshore & Offshore Marine Terraces – San Onofre Area Rotational Landslides in coastal cliffs Wave notched cliff Translational Landslides in coastal areas Tsunami Risk at SONGs Honshu Earthquake 3/2011 Magnitude 9.0 (USGS) Depth 19.9 mile http://neic.usgs.gov/neis/eq_depot/2011/eq_110311_c0001xgp/neic _c0001xgp_l.html Most earthquake damage is due to ground shaking. Tsunamis also can significant damage in coastal areas. December 26, 2004—Indian Ocean tsunami. March 11, 2011—eastern coast of Japan. Fukushima power plant damage The Fukushima nuclear power plant was damaged. Water breached the seawalls placed to protect the plant. Hydrogen explosions destroyed the reactor buildings. Megathrust earthquakes Dana Point Harbor Capistrano Formation at Dana Point Harbor Capistrano Formation at Dana Point Harbor Capistrano Formation at Dana Point Harbor Submarine Canyons Turbidite Deposits http://eqdoc.home.netcom.com/salt2.html Dana Cove Fault near Cannons Restaurant at Dana Pt. Harbor Laguna Beach at Heisler Park Volcanic dikes cutting through sedimentary rocks Sedimentary rock with tafoni weathering at Heisler Park .