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chapter 11 coastal erosions
Terms in this set (43)
Understand why the east coast of North America is considered tectonically passive
-East Coasts of North America is considered tectonically passive because it is not close to a convergent boundary.
-Tectonically passive coasts typically have wide continental shelves with barrier islands and sandy beaches.
Understand why the west coast tectonically active
-West Coasts are tectonically active because they are close to transform boundaries.
-mountain building produces coasts with sea cliffs and rocky shorelines.
Understand what produces waves and the three factors that affect wave size.
-Caused by offshore winds producing friction over water
-3 factors that affect wave size: wind speed, duration of wind, fetch (Distance wind blows over water surface).
What is wave motion like out in the ocean?
-It is circular out in the ocean
-Circles decrease in diameter with increasing depth
-waves move in open ocean with little energy loss
-energy is spent on reaching coastline
What happens to the wavelengths, wave velocity, and wave height as waves hit the coast?
-Wavelength and velocity decrease, wave height increases as waves hit the coast.
What is global, or eustatic, sea level?
-changes are long term affected by changes in amount of water in ocean.
How do global temperatures specifically make it change? (When global temperatures cool
enough, does that cause a eustatic sea level rise, or fall? What about when temperatures warm up?)
-temperature increases cause volume of water to expand, sea level to rise
-temperature decreases cause more ice to form on land
-volume of water in ice sheets, glaciers increase, ocean water decreases (when it gets cold enough for long enough we get an ice age.
How does tectonic activity make eustatic sea level change?
-changes ocean basin shape over long period of time
What is relative sea level and what three major factors did we look at that can change it?
-short term changes caused by such things as:
1.) glacier or ice sheet melt (isostatic rebound) or earthquakes (uplift of plate boundaries) can cause uplifting of land.
-decrease in relative sea level
2.) tides caused by gravitation pull on the moon cause daily and seasonal changes
3.) weather conditions
-winds and storm surges
How do rip currents form and which way do they flow?
-waves pile up and water becomes concentrated in narrow zones.
-escape requires swimming parallel to shore
-currents that move away from shore.
What is a beach budget?
-longshore and beach drift bringing sediment from upshore
-local eroision of dunes and cliffs
-longshore and beach drift bringing
-sediment away from shore
How does a beach change when input exceeds output, and vice versa?
-beach grows when input exceeds output
-beach erodes when output exceeds input.
Effects of coastal processes: Cliff Erosion: In what three ways do human activities increase the erosion rates of cliffs?
-Increase surface runoff
-increase groundwater discharge
-addition of weight to cliff
How do we minimize the effects of coastal hazards?
-structures built parallel to coastline to help retard erosion and protect buildings from damage
-vertical design reflects waves and redirects energy to shore
-promotes beach erosion
What is hard stabilization
-structures built perpendicular to shoreline usually in groups
-traps sand from longshore drift
-causes increased erosion in downdrift area
the difference between a jetty and a groin is that jetties are meant to stabilize a channel (such as the one we saw between the two barrier islands on our in-class exercise) whereas groins can be placed one after another along a stretch of beach and are intended to trap sand and stabilize a sandy beach. Both are
placed perpendicular to the beach
What is soft stabilization?
-adding sand to replace sand that has eroded
-aesthetically preferable to hard stabilization
What is a barrier island?
-long narrow islands of sand separated from mainland by lagoon or bay
What are the five principles of living with coastal erosion?
1.) Coastal Erosion is a natural process rather than a natural hazard
2.) Any shoreline construction causes change. This change interferes with natural processes and produces a variety of adverse secondary and tertiary changes.
3.) Stabilization of the coastal zone through engineering structures protects property, not the beach itself. Most protected property belongs to relatively few people at a larger expense to the general public.
4.) Engineering structures designed to protect a beach may eventually destroy it.
5.) Once constructed, shoreline engineering structures produce a costly trend in coastal development that is difficult, if not impossible, to reverse.
Beach Form and Processes
-beach: is a landform consisting of loose material, such as sand or gravel, which has accumulated by wave action at the shoreline.
-type of beach material depends on source of sand
-white beaches from shell and coral
-black beaches from volcanic rocs
-light brown beaches from quarte and feldspar from rocks such as granite.
-sand movement parallel to shore. consist of: beach drift, and longshore drift.
Human Interaction:Atlantic Coast
-characterized by barrier islands
-long narrow islands of sand separated from mainland by lagoon or bay
-removal of coastal dunes
-increased vulnerability to storms
-interrupts longshore drifts
-increases erosion at some locations
Human Interaction: Gulf Coast
-gulf coast erosion due to
-coastal engineering structures
-subsidence due to groundwater or petroleum withdrawal
-damming of rivers
-increased hurricane intensity due to climate change
coastal areas are dynamic environments that vary in their topography, climate, and organisms
continental and oceanic processes converge to produce landscapes that are capable of rapid change.
some american and canadian coasts are significantly influenced by climate and organisms
-coastlines in temperate regions are influenced by marsh vegetation and subtropical and tropical shores are affected by growth of mangroves and offshore coral reefs
impact of hazardous coastal processes is considerable because many populated areas are located near the coast
Most serious coastal hazards are the following
-strong coastal currents, including rip currents generated in the surf zone and tidal currents in narrow bays and channels
-coastal erosion, which continues to produce considerable property damage that requires human adjustment
-storm surge from tropical and extropical cyclones, which claims many lives and causes enormous amounts of property damage every year
-tsunamis, which are particularly hazardous to coastal areas in the Pacific Ocean
-a single crest of an oscillation of the surface of the ocean that is much higher than usual. Commonly caused by the constructive interference of smaller waves
are linear structures placed perpendicular to the shore, usually in groups called groin fields
is designed to intercept waves and provide a protected area or harbor for mooring boats and ships
usually built in pairs, perpendicular to the shore at the mouth of a river or at the entrance of an inlet to a bay or lagoon.
-designed to keep a ship or boat channel open and in a fixed location, with minimal dredging to remove sediment
-that batter the coast are generated by offshore winds, sometimes thousands of kilometers from where the waves reach the shoreline
-wind blowing over the water produces friction along the water surface. Because the air is moving much faster than the water, the moving air transfer some of its energy to the water and produces waves.
waves vary in both their size and shape
the size of waves in the ocean or on a lake depends on a combination of the following:
-the velocity or speed of the wind; the stronger the wind speed, the larger the waves
-the duration of the wind. winds that last longer, such as during storms, have more time to impart energy to the water, thereby producing larger waves.
-the distance that the wind blows across the water surface. This distance is referred to as the fetch. A longer fetch allows larger waves to form. The relationship is one reason that waves are generally larger in the ocean than in a lake.
3 parameters describe the size and movement of a wave
1.) wave height, which is the difference in height between the trough and a crest of a wave.
2.) wavelength, the distance between successive waves to pass a reference point
3.) wave period, the time in seconds for successive waves to pass a reference point, and to describe the electromagnetic radiation and wave height of seismic waves as one indicator of earthquake magnitude.
To understand how waves transmit energy through the water
it is useful to study the motion of an object on the water surface and one below the surface.
-the up-and-down movement of beach material in the swash zone causes sediment to move along a beach in a zigzag path
to the transport of sediment by ocean currents that flow essentially parrallel to the shoreline. These currents, called longshore currents, are the primary mechanism for littoral transport.
longshore drift and beach drift occur when waves strike the coast at an angle.
The term updrift and downdrift are often used to indicated the direction in which sediment is moving or accumulating along the shore.
the direction of littoral transport along both the east and west coasts of the US is most often to the south, although it can be quite variable.
Geographic regions at risk
-plus shores of Great Lake
Linkage to other Natural Hazards
Natural Service Functions
-beauty of the coastal zone results in part from wave action and erosion
-stunning cliffs, rocky headlands and sea arches
-without erosion of dunes, cliffs and bluffs inland from the beach or the erosion of updrift beaches, there would be little sand to form a beach
-longshore drift, maintain sandy beaches on all coasts, including lake shores
-renews these ecosystems and maintains their diversity
-provide us with much-loved recreational opportunities, including swimming, surfing, sailing, fishing, and sunbathing
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