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

Geology of Dana Point area

Mark Bordelon Irvine Valley College March 2012

Subduction of the Farallon Plate 100 m.y. ago

Continental Margins Where land meets the ocean

Margins near plate boundaries are ―active.‖

Margins far from plate boundaries are ―passive.‖

Fig. 3.11

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

Basin

Up block Up block

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

c

Biochemica

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

5 major coastal cells within 200 miles

Coastal Cells in S. Calif.

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

http://eqdoc.home.netcom.com/salt2.html

Turbidite Deposits

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