Coasts categories, sea level changes, and defenses
What is a Coast?- A zone where the land meets the sea. Extends from the shoreline to the first major terrain change. They
are constantly altered in response to conditions around them, and the nature of the tides.
Global Sea-Level Change
There are three causes of global change in sea level
1. An increase or decrease in the world’s ice sheets and glaciers
2. A rise or fall in ocean temperature
3. Any change in the size of the ocean basins
Glaciers and Ice Sheets
-As climate heats up: Glaciers begin to melt, Sea levels rise, Lower coastal areas are covered with water, Effects of
Global Warming
-As climate cools: More glaciers form (or become larger), More water is taken from the ocean, Sea levels drop, More
coastal areas are exposed
Ocean Temperature
► Heating of ocean’s surface…Warm water is less dense, Warm water expands, Total volume of oceans increases
► Temperature Change During La Nina
Ocean Basins
► Any change in the size or shape of an ocean basin can effect ocean levels
► Ex. Change in the activity of the mid-ocean ridge may drive long-term sea level change
► New crust swells, pushing up on ocean water
Local Sea-Level Change
► Occurs when an area of land rises or falls
► Caused by:
 Tectonic uplifting of land – occurs in subduction areas
 Glacial rebound – gradual rise of land after an ice sheet that weighed it down has melted
 Southeast Alaska has risen over 18 ft in 250 years.
 Vegetation is changing as wetlands expand
Sinking Coastal Areas
► Occurs where a heavy load of coastal sediments pushes down the bedrock underneath it
► Also occurs with volcanic islands: Once created, they cool, compact, and contract while the sea floor warps
downward underneath them
Drowned Coasts
► AKA submergent coast
► Caused from a global or regional sea level rise- Ex. Chesapeake Bay
Types of Drowned Coasts
► Rias- is a coastal inlet formed by the partial submergence of an unglaciated river valley. It is a drowned river valley
that remains open to the sea
 Found mostly in northwestern Europe, eastern US, and Australia
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Coastal river valleys are drowned
Forms a series of wide estuaries separated by long peninsulas
► Fjords- is a long, narrow inlet formed when a glacier cuts a U-shaped valley in the surrounding bedrock.
 Found in coastal Norway, Chile, Canada, New Zealand
 One or more deep glacier-carved valleys are drowned
Emergent Coasts
► Where land is uplifting faster than the sea is rising
► Typically rocky
► Found on the US Pacific Coast, Scotland, Scandinavia, New Zealand
► Causes:
 Activity at the edge of a tectonic plate
 Glacial rebound
► Former sea floor areas may become exposed above the shoreline
► Former beaches end up far inland, or on clifftops
► Marine terraces form
 Staircase-like structures created by uplift and waves cutting flat platforms at the bases of cliffs
► San Clemente Island, California
Past Change
► Rocks and fossils near shorelines are studied by scientists to calculate past sea-level changes
► Ocean sediments are analyzed to calculate past ocean temperatures and climate properties.
Global Warming Effects
► The earth’s climate changes, regardless of humans
► But, are humans speeding up the changes?
Global Warming
► Sea levels are rising by 1/8 in. (2.9 mm) per year, and have been since 1900.
► The temperature of the Earth’s atmosphere and oceans has risen .07-1.4o F since 1900
► Because there are no other convincing explanations of what is causing the sea level rise, most scientists believe
that the cause is global warming (human-caused climate change)
The Future of Global Warming
► Predictions from the Intergovernmental Panel on Climate Change:
 By 2099, there will be a further sea-level rise of 4 ½ - 35 inches.
► Some small island nations will be covered with water
► Low-lying coastal areas will be effected
Effects of Global Warming
► Glacier Retreat- Temperatures are rising, glaciers are melting
► Submerging Islands- waters rise, islands get flooded- The island nation of Kiribati, located in the central tropical Pacific
Ocean.Kiribati has been facing rising waters by as much as 5 mm per year since 1991. This phenomenon has also
been causing the high salinization of its fresh water. Global warming is being blamed for what has been happening
to the island nation that is one of the lowest spots on earth, found between Hawaii and Fiji.
► Populations at risk- threats to human health through increased droughts, hurricanes, tornadoes, and floods
► Animals in Danger
Top 10:
1. Clownfish- rising CO2 the oceans turn acid which disrupts the clownfishes’ sense of smell and their ability to
find the anemones
2. Emperor penguin- are losing the sea ice they need for mating and chick-rearing.
3. Koala bear-under threat from drought, forest fires and the decreasing nutritional content in Eucalyptus leaves
because of too much carbon dioxide.
4. Beluga whale- more ships come into the area and it is exploited for minerals like oil and gas
5. Leatherback turtle-cannot breed on beaches increasingly affected by storms caused by climate change
6. Quiver tree-cannot cope with drought
7. Staghorn coral-Ocean acidification will also bleach & the acid weakens the skeletons
8. Arctic fox- the ice they rely on for food and pup-rearing retreats
9. Ringed sea- the ice they rely on for food and pup-rearing retreats
10. Salmon-threatened by increases in water temperature, which reduces water’s oxygen levels and disrupts
their breeding efforts
Coastal Landscapes
► Coasts are shaped by :
 Sea-level change
 Wave erosion
 Weathering
 Erosion and deposition by rivers
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► Coastal features are made by:
 Living organisms- Coral and oyster reefs
 Humans- Coastal defenses, Artificial islands, harbors
Classification of Coasts
► Primary Coasts
 Formed from land-bases processes
► Sediment deposition from rivers
► Land erosion
► Volcanic action
► Rifting and faulting of crust
► Sea-level change (drowned and emergent coasts)
► Wind-deposited sand, glacial till, seaward end of glaciers
Glacier advance and retreat
Lava flow
Tectonic faulting
► Secondary Coasts
 Shaped by:
► ocean changes
► Activities of organisms- Corals, mangroves, people
► Artificial Coast
► Some coasts display both primary and secondary features, so fit into an intermediate category
 Ex. Emergent coasts where heavy marine erosion has taken place
Wave-Erosion Coasts
► Type of secondary coast, consisting of heavily wave-eroded cliffs
► Wave erosion has two effects:
 Erodes the rock away
 Compresses air within cracks of the rocks, which shatters when they re-expand.
Erosion and Headlands
► As waves hit headlands, features develop in a classic sequence:
1. Deep notches and sea caves form at the bases of cliffs on each side of the headland
2. Caves widen and cut through, forming an arch
3. The roof of the arch falls, leaving an isolated rock pillar (stack)
4. The stack is eroded down to a stump.
Marine-Deposition Coasts
► Formed from sediment brought to a coast by:
 Rivers
 eroded from headlands
 moved from offshore by waves
► Sediments are deposited by longshore drift.
 Sediments are moved along the shore as waves crash at one angle, and drag back down at a different
angle
 Sediments settle and build up at areas where the waves are smaller
 Features include: spits, baymouth bars, and barrier islands
► Spit
 A sandy peninsula with one end attached to the land
► Baymouth Bar
 When a spit extends across the mouth of a bay or estuary
► Barrier Island
 Long, thin islands parallel to the coast
Coastal Defenses
► Engineering techniques aimed at protecting coasts from the sea
 Protection from flooding dangers
 Protection from continuous and gradual erosion of certain coasts
 Only a temporary fix…in the end, the sea will triumph!
Coastal Defense Approaches
► To prevent flooding:
 Dams and tidal barriers
 Development of natural barriers (salt marshes)
 Managed retreat (allowing some areas of the coast to flood), forming a protective marsh
Hard vs. Soft Engineering
► Hard engineering techniques:
 Can be effective for long periods of time
 Expensive
 Can increase erosion on other areas
 Will have to be rebuilt at some point
 Examples:
 Sea walls, breakwaters, groynes (jetties)
► Soft engineering techniques:
 More environmentally friendly
 Temporary
 Encourages the development of coastal dunes (which provide natural protection)
► Ex. Beach nourishment
Sea Walls
► Designed to reflect wave energy
► Protects the land behind it
► Increases erosion of the beach in front of it
Rock Groynes
► A pile of large rocks built out from the shore
► Slows erosion by causing a local buildup of sand
► Can cause or increase erosion in other areas around it
Dune Stabilization
► Provide valuable protection from erosion if they can be prevented from shifting
► Wild grasses are planted to maintain stability
► Can shift over time
Beach Nourishment
► Adding large amounts of sand to a beach
► Waves and tides spread the sand along the coast, helping to build it up
Geotubes
► Long container made of plastic and filled with sand and water
► Reduce coastal erosion and protect beach fronts
Dams and Storm-Surge Barriers
► A series of dams and movable storm-surge barriers
► The ocean groyne built to hold sand on one beach, increases erosion on the other beach
Crumbling Coasts
► As of 2000, 87,000 houses in the US are in danger of falling into the sea by the year 2060
► In California, 86% of the coast is actively eroding
► Eastern coasts in England show erosion at 6 feet a year