The Coast

• temporary junctions between land and sea

• are subject to change– waves, currents, tides, biological processes,

tectonic activity

• position changes as sea-level does

Sea level 18,000 years ago during last ice age

If sea level rises 60m (200ft) and floods 250 km (160 mi) inland

Classification of Coasts

• Erosional Coasts– Dominant process is removal of material

– Rocky shores of Maine and central California

– Tectonic uplift

• Depositional Coasts– Dominant process is the accumulation of material

– Sandy beaches of Jersey to Florida and Southern California

– subsidence

Erosional Coasts

• Land sources of erosion:– Stream erosion

– Wind abrasion

– Plant roots

– Freezing/thawing of water in rock cracks

• Marine sources of erosion:– Waves: water itself or tossed rocks etc

– Tides

– Marine organisms

Erosional Coasts

• Effects of erosion depend on:– Hardness of rock

• Sandstone erodes quickly, granite erodes slowly

– Wave energy– Tidal range

–Figure 10.4

Sea cliff and Wave cut platform

Sea Cave – La Jolla, CA

–Figure 10.5

Depositional Coasts

• Composed of sediment rather than rock- such as beaches

• Built up by biological activity – such as coral reefs, salt marshes and mangrove swamps

–Figure 10.7

–Fig. 11-23, p. 261

–Great Barrier Reef, Australia

–Mangrove coast, Florida

Erosional vs Depositional Coasts• Some coasts show characteristics of both

– Central California is erosional but southern California is depositional

• Erosional Coast can become depositional coasts– As erosion turns rock to sediment and deposits

it on shore

• Depositional Coasts can still experience erosion

Estuaries

• Body of water partially surrounded by land where fresh water from a river mixes with ocean water

Estuaries

• Great biological productivity and diversity– Protection from wave shock– Variety of habitats (salt marshes, mangrove

swamps, seagrass meadows, etc)– Availability of nutrients

• Used as nurseries by many species

Estuaries

• Characterized by their circulation pattern– Shape of estuary– Volume of river flow– Tidal range

• Salt wedge estuaries

– Rapid river flow

– Low tidal range

– Hudson River, Mississippi River

•Well-mixed estuaries

–Slower river flow

–High tidal range

–Columbia River (Washington and Oregon)

• Partially mixed estuaries

– Rapid river flow

– High tidal range

– Chesapeake Bay (Maryland and Virginia)

Beaches

• a zone of loose particles that covers part of the shore

• extends from a landward limit – cliff, permanent dunes, seawall

• extends to the seaward limit where movement of sediment on and offshore ceases

–Figure 10.1

Beach Profiles

• Steepness of beaches change with seasons and storms– Summer and calm periods build up beaches– Winter and storms erode and flatten beaches

–Figure 10.2a

–Figure 10.2d

–Fig. 11-13c, p. 254

Beach Profiles

• Steepness depends on sediment size– Beaches with larger particles tend to be steeper– Smaller particles result in flatter beaches

Beaches

• exist in a delicate balance between accumulation and destruction

• Waves can transport sand onshore or offshore

• Longshore currents transport sand along the coastline

–Figure 10.3b

–Figure 10.7

–Figure 10.8

–Martha’s Vineyard, MA

–Great Rock Beach, CA

Barrier Islands

• Are essentially large sand bars

• Protect the coast behind them

• Very unstable themselves

–Figure 10.9

–Tom’s River, NJ

Heavily developed barrier island: Ocean City, MD

–Figure 10.10

Barrier Island Migration

–Fig. 11-19, p. 258

Human Impact on Beaches

• Attempts to “save” beaches or property often fail or make matters worse

–Figure 10.18: Groins

–Figure 10.19

Groin Field

Cape May, NJ

–Figure 10.20: Jetties

–Figure 10.21

–Santa Cruz Harbor, CA

Break water

Santa Monica, CA

–Figure 10.24: Seawalls

Alternative:

Beach Replenishment

–Figure 10.26

–Figure 10.B: Relocation