Coastal Processes and Landforms

The Coastal Environment

 The World Ocean covers 71% of Earth’s surface, and the world’s

shoreline

is of enormous length  Earth’s coastlines have tremendous resource, and they are biologically and geomorphically

diverse

 Their

spectacular scenery

bring in more

tourists

than any other natural environment, and continue to attract

new residents

 But they are also subject to any array of

natural hazards

, and human

-

induced environmental problems; ironically, some of our most

polluted waters

are found in coastal locations 

Global warming

and resulting

sea level rise

will have profound consequences for

coastal zones

The Coastal Zone: Definitions

Coastal Zone

: General region of interaction between the land and the ocean

Shoreline or Coastline

: Constantly changing contact between the ocean surface and the dry land

Sea Level

: Average position of the ocean shoreline from which all elevations are measured

Swash

: The thin sheet of water rushing towards the shoreline

Backwash

: The return flow of water to the ocean

Nearshore Zone

: Comprises

Breaker Zone, Surf Zone and

Swash Zone

(See Fig. 17.1, p. 407 in Text)

Offshore Zone

: Undefined zone seaward, beyond the breaker zone

Continental Shelf and Continental Slope

Waves and Currents

Waves

: are travelling, repeating forms of alternating highs and lows called

wave crests

and

wave troughs –

induced by

Wind Currents

: horizontal movement of ocean water, usually in response to atmospheric circulation  also,

rip currents, long shore currents

Wave Refraction – waves change directional trend as they approach shore.

Raglan, New Zealand

Basic Concepts

I. Repeated sea level changes in the past • Estimated 422 ft. rise since 18,000 years ago • specific landscapes submergent (Passive) or emergent (Active) depending on tectonic change II. Waves and resultant currents erode, transport, and deposit sediment load.

• rocky headlands • beaches III. Tides affect all coastal life but have little topographic effect.

• tidal bore/tidal wave/tsunami

Submergent vs. Emergent Coastlines

• During the ice ages (or glacial periods) sea level sinks as more water is tied up in glaciers • During interglacial periods sea level rises, flooding many river valleys, creating bays and estuaries •

Submergent Coastlines

 Rias: drowned river valleys; Fjords: drowned glacial valleys • Sea levels rise also causes many features of the former shore lie underwater • Also known as Passive-margin Coasts – e.g., Atlantic Coast – because tectonic activity occurs in the middle of the ocean, and the coast is tectonically passive.

Submergent Coastlines

Sea level rise inundated many coastal valleys creating bays and estuaries. These coasts are often referred to as

Ria

coastlines .

Estuary

– An arm of the sea that extends inland i.e., an inlet) to meet the mouth of a river.

Emergent Coastlines

where water level has fallen, or land has risen due to tectonic activity In areas with “rapid” tectonic uplift,

Emergent

Coastlines and cliffs are common, and bays are rare Also called Active- margin Coast – e.g., Pacific Coast Tectonic forces lift coastlines faster than sea-level rises. Dramatic sea cliffs and marine terraces tower above the sea. Also, sea stacks.

Most activity occurs along active subduction zones and transform plate boundaries.

COASTAL PROCESSES AND LANDFORMS

Coastal Erosion – dependent on wave size, angle, and frequency. Focused where waves contact coastline.

• Headlands, sea cliffs, bluffs, sea stacks, natural bridges • Beach Erosion

Coastal Transportation –

Large waves move beach sand offshore. Small waves push it back onshore.

• Wave action creates strong currents parallel to shore – Longshore currents, and longshore drifting.

 Also Littoral drifting and beach drifting.

Coastal Deposition –

where wave action is reduced, beaches and dunes form.

• Beaches, dunes, sand spits

Coastal Erosion

Hydraulic action

: Sheer physical force, the pounding of waves against coastal rock material.

Abrasion

: The process of wearing down or rubbing away by means of friction.

Isla Vista Beach, October 2001

Isla Vista Beach, December 2002

Beach Erosion

Formation of

Marine Terrace

Marine Terraces

Point Reyes National Seashore California

Sea Stacks

Port Campbell National Park, Victoria, Australia

Natural Bridges and Arches Port Campbell National Park, Victoria, Australia

Erosional Landforms

1. Sea Cliffs

: When Waves pound directly against steep land

2. Sea Caves

: Erosion, corrosion and hydraulic action along lines of weakness

3. Sea Arches

: 2 caves meet from each side of hydraulic action of a headland

4. Sea Stacks

: A resistant pillar is left standing – the remnant is called a sea stack

5. Marine Terraces

: Formed by tectonic activity uplift out of reaches of wave action

6. Headlands

: Prortruded land, flanked by receding bays

Depositional Landforms

1. Beach

: Landform of coastal deposition, continuous with the mainland  Sandy beaches, Pebble and boulder beaches, White coral reef beaches, Black sandy beaches – in volcanic Big Island, Hawaii

2. Spits

: Coastal depositional landforms connected to the mainland at just one end

3. Barrier beaches

: long depositional feature constructed parallel to mainland, protection from direct wave attack

4. Lagoon

: Body of water partially or fully enclosed by

baymouth bar 5. Tombolo

: Strip of sediment connecting mainland to an island

Tombolo

Tombolo

Sand Spit

Sand Spit

Barrier Islands

Barrier Islands

Point Reyes National Seashore, California

Point Reyes Lighthouse

Islands

Types of Islands

1. Continental Islands – separated from mainland due to shore submergence 2. Oceanic Islands – volcanic islands 2. Atoll – coral formation

Tropical Coasts

Factors Correlated with Healthy Coral Reef Growth

• • • • • Water temperature range: 18 – 29  C Normal seawater salinity: 32 – 35 ‰ Clear, transparent water Little or no sedimentation Vigorous water motion

Tropical Mangroves

Mangroves create tidal forests. These rich ecosystems provide habitat for countless creatures and help to stabilize and, by catching sediment, even create coastline.

Tides

Low Tide, New Brunswick

Tides

Tide Cycle Tides rise and fall with the rising moon, an interval of 24 hours and 50 minutes. There is a bulge on both sides of the earth. Thus

two high tides

each cycle.

Flood tide

(low to high) takes 6:13 and then

ebb tide

(back to low) is another 6:13.

Tides

Tide Range Tide range dependent on relative position of earth, moon, and sun.

Spring Tides -

highest tidal range

Neap Tides -

lowest tidal range Occurs every 2 weeks

Tidal Patterns in the U.S.

Tides

Not significant as a geomorphic agent, but can be very consequential when coinciding with storm surges or tsunamis