Download Chapter 12, Coasts

Coasts
Part 2
Classifying Coasts/Beaches
About 44% of the world’s population lives
within approximately 93 miles of the ocean.
Approximately 39% of the U.S. population
lives in counties directly on the coastline.
Coast & Shore
• Coastal areas join land & sea
• Shore = Place where ocean meets land (Ex.
sandy beach)
• Coast or Coastal zone = More than just the
shore; It is the areas affected by the
processes occurring at the ocean-land
boundary (Ex. beach, dunes, marshes, cliffs, &
offshore sandbars)
Coast & Shore
A coast is an active place!
“There is nothing permanent except
change” ~ Heraclitus 540-470 BC
Coast & Shore
Coasts can be affected by any of the following:
•Breaking waves
•Rise & fall of the tides
•Discharge of river sediment
into the ocean
•Longshore currents
•Ocean storms
•Biological processes
•Change in sea level
•Sinking & rising of the land
(tectonic processes)
•Human activity
Erosion & Deposition
•Erosion is the process by which the Earth’s
surface gets worn down. Erosion can be
caused by wind, water, or ice.
•Coastal erosion occurs along beaches and
shorelines.
•The process by which transported sediments
are left in new locations is called deposition.
Erosional Features
Inlet: A narrow body of
water between islands or
leading inland from a larger
body of water, often leading
to an enclosed body of water ,
such as a sound, bay, lagoon,
or marsh
Bay
Bay: A body of water
partially enclosed by land, but
with a wide mouth, giving
access to the sea
Inlet
Erosional
Features
All three of these
features are
formed by wave
erosion.
Sea cave
Sea arch
Inlet
Sea stack
In order of increasing erosion…
1) Sea cave
2
1
2) Sea arch
3) Sea stack
3
Erosional Features
Headland
Sea Stack
Sea cave
Headland
Sea arch
Headland: A section of land
jutting out into the sea,
formed when different rocks
erode at different rates
Erosional Features
Lagoon
Lagoon: A shallow body of water that does not receive
significant freshwater inflow and that is separated from
the open ocean by a barrier island or coral reef
Depositional Features
Beach
Depositional Features
Sand dunes with vegetation/grasses
Depositional Features
Barrier island
Mainland
Lagoon or sound
Barrier island
Ocean
Depositional Features
Barrier island: A long,
often narrow accumulation
of sand that is separated
from the mainland by
open water
(lagoon, bay,
estuary) or
by salt
marshes
Depositional Features
Spit
Depositional Features
Spit: An extended stretch
of beach material that
projects out to sea & is
joined to the mainland
at one end
Depositional Features
Tombolo
Depositional Features
Tombolo: A spit
connecting an island to
the mainland
Depositional Features
Delta: Landform that is
formed at the mouth of a
river, where the river flows
into an ocean, sea, estuary,
or lake
Review of Depositional Features
Classifying Coasts
Coasts can be classified as Primary or
Secondary:
Primary Coasts = Formed by terrestrial
processes not related to the ocean (nonmarine processes); Owe their character &
appearance to land erosion, deposition of
sediments, & other processes that occur on
land.
Classifying Coasts
Examples of primary coasts:
•Volcanic coasts like Hawaii
•Coasts shaped by earthquakes like Alaska, San Francisco
•Coasts formed by land erosion when glaciers deposit
sediment when ice melts
•Coasts formed by land processes where sediment washes
off the land to build out the coast (when rivers form
deltas)
•Wind deposition coasts with sand dunes
•Land erosion coasts like Puget Sound
& Chesapeake Bay, from drowned river valleys
Primary Coasts
Chesapeake Bay
Delta
Coast formed by glaciers
Volcanic coast
Classifying Coasts
Secondary Coasts = Coasts significantly
changed by wave action & other marine
processes or marine organisms
Classifying Coasts
Examples of secondary coasts:
•Coasts formed by biological activity (coral reefs,
mangrove forests, oyster reefs)
•Wave erosion coasts like the Pacific coast
•Marine deposition coasts like sandy beaches & barrier
islands
Secondary Coasts
Wave erosion coast
Wave erosion coast
Sandy beach
Mangrove coast
Some coasts can show
characteristics of both primary
and secondary coasts!!!
Primary: Wind
deposits sand to
create dunes
Secondary:
sandy
beach forms
when
waves deposit
sediment
Beaches
A Beach is the most familiar feature of a
secondary coast. A beach is a zone of
loose particles that covers part or all of a
shore.
Beaches
Water from waves washing onto a beach is called
swash – carry particles onshore and increases
beach slope.
Water returning to the ocean is called backwash.
If the water carries back the same amount of
material as it delivered onto the beach, the beach
slope will be in equilibrium & the beach will not
become larger or smaller.
Typical Beach Profile
Typical Beach Profile
Backshore = The zone of the beach above the
high tide line
Typical Beach Profile
Nearshore = The zone that extends from the
swash zone to the start of the offshore zone
Typical Beach Profile
Offshore = Extends seaward beyond the breaker
zone to the edge of the continental shelf
Typical Beach Profile
Longshore or sand bar = submerged or exposed
accumulations of sand lying parallel to the shore
Typical Beach Profile
Exposed sand bar at low tide
Typical Beach Profile
Surf zone = the section of the coastal zone
between the coastline & the breaker zone
Typical Beach Profile
Breaker zone = the zone where waves begin to
break
References
www.nasa.gov
www.photolib.noaa.gov