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