Chapter 15 Concepts
What is a beach? Distinguish between beach face and berm.
- A beach is an accumulation of sediment found along the landward margin of the ocean or lake - A berm is a relatively flat platform often composed of sand that is adjacent to coastal dunes or cliffs and marked by a change in slope at the seaward edge, whereas a beach face is the wet sloping surface that extends from the berm to the shoreline
Describe the process of coastal upwelling. Why is an abundance of marine life associated with these areas?
- Coastal upwelling occurs when winds blow toward the equator and parallel to the coast. Coastal winds combined with the Coriolis effect cause surface water to move away from the shore. As the surface layer moves away from the coast, it is replaced by water that "upwells" from below the surface, which brings colder water near the shore - An abundance of marine life is associated with these areas because upwelling brings greater concentrations of dissolved nutrients to the ocean surface, promoting the growth of microscopic plankton, which supports extensive populations of fish and other marine organisms
Name the five subtropical gyres and identify the main surface currents in each.
- North Pacific Gyre: North Equatorial Current, Kuroshio Current, North Pacific Current, California Current - South Pacific Gyre: South Equatorial Current, Peru Current, West Wind Drift, East Wind Drift - North Atlantic Gyre: Labrador Current, E. Greenland Current, Norwegian Current, Gulf Stream, North Atlantic Current, Canary Current, North Equatorial Current - South Atlantic Gyre: South Equatorial Current, Benguela Current, Brazil Current - Indian Ocean Gyre: Aguthas Current, West Australian Current, North Equatorial Current, South Equatorial Current, Leeuwin Current
How do ocean currents influence climate? Provide examples.
- When currents from low-latitude regions move to higher latitudes, they transfer heat from warmer to cooler areas on Earth - The North Atlantic Current keeps Great Britain and much of northwestern Europe warmer during the winter than one would expect for their latitudes - The Cool Benguela Current off the western coast of southern Africa moderates the tropical heat along this coast. Walvis Bay, a town adjacent to the Benguela Current, is 5 degrees Celsius cooler in summer than Durban, which is 6 degrees latitude farther poleward but on the eastern side of South Africa, away from the influence of the current.
List three ways that barrier islands may form
- some originated as spits that were subsequently severed from the mainland by wave erosion or by the general rise in sea level following the last episode of glaciation - some were created when turbulent waters in the line of breakers heaped up sand that had been scoured from the bottom - some may be former sand-dune ridges that originated along the shore during the last glacial period, when sea level was lower
What is the primary driving force of surface ocean currents? List two additional factors that influence surface currents.
- the primary driving force of surface ocean currents is the distribution of major landmasses - gravity and friction between the ocean and the wind that blows across its surface influence surface currents
Distinguish among shore, shoreline, coast, and coastline
- the shoreline is the line that marks the contact between land and sea, whereas the shore is the area that extends between the lowest tide level and the highest elevation on land that is affected by storm waves - the coast extends inland from the shore as far as ocean-related features can be found, and the coastline marks the coast's seaward edge
Describe 2 ways in which waves cause erosion
- wave impact and pressure - abrasian
List 3 factors that determine the height, length, and period of a wave
- wind speed - length of time the wind has blown - fetch (the distance that wind has traveled across open water)
Describe the ocean's conveyor-belt circulation
A simplified model of ocean circulation is similar to a conveyor belt that travels from the Atlantic Ocean through the Indian and Pacific Oceans and back again. In this model, warm water in the ocean's upper layers flows poleward, converts to dense water, and returns equatorward as cold deep water that eventually upwells to complete the circuit
What is the effect of wave refraction along an irregular coastline?
As waves first touch bottom in the shallows along an irregular coast, they are slowed, causing them to bend (refract) and align nearly parallel to the shoreline
What are two alternatives to hard stabilization and potential problems associated with each?
Beach Nourishment - not a permanent solution to the problem of shrinking beaches because the same processes that removed the sand in the first place will eventually remove the replacement sand as well - can be very expensive Relocation - people with significant shoreline investments aren't able to rebuild and defend coastal developments from the erosional wrath of the sea
List at least two examples of hard stabilization and describe what each is intended to do. How does each affect sand distribution on a beach?
Groins - built to maintain or widen beaches that are losing sand - causes the current to erode sand from the beach on the downstream side of the groin, sand-starving the longshore current beyond the groin Breakwaters - build to protect boats from the force of large breaking waves by creating a quiet water zone near the shore - reduced wave activity along the shore behind the structure may allow sand to accumulate, causing the boat anchorage to fill with sand while the downstream beach erodes and retreats Seawalls - designed to armor the coast and defend property from the force of breaking waves - the beach to the seaward side of the seawall experiences significant erosion and may even be eliminated entirely
How is a marine terrace related to a wave-cut platform?
If a wave-cut platform is uplifted above sea level by tectonic forces, it becomes a marine terrace
Why is deep-ocean circulation referred to as thermohaline circulation?
The density variations that cause deep-ocean circulation are caused by differences in temperature and salinity
Why do waves that are approaching the shoreline often bend?
The part of the wave nearest the shore touches bottom and slows first, whereas the part of the wave that is still in deep water continues forward at full speed
Briefly describe what happens when storm waves strike an undeveloped barrier island
When a storm occurs, the barriers absorb the energy of the waves primarily through the movement of sand
What observable features would lead you to classify a coastal area as emergent?
exposed wave-cut cliffs and marine terraces above sea level
Describe the motion of a floating object as a wave passes
it moves not only up and down but also slightly forward and backward with each successive wave
Distinguish between neap tides and spring tides
neap tides have less of a tidal range than spring tides
How might building a dam on a river that flows to the sea affect a beach?
the building of dams interrupts the natural flow of material to the coast and the reservoirs effectively trap the sand that would otherwise nourish the beach environment
Why is the shoreline considered an interface?
the shore is the dynamic interface among air, land, and sea because these different parts interact at the shoreline
How does a wave's speed, length, and height change as it moves into shallow water and breaks?
the speed and length of a wave diminishes and the wave steadily grows higher until it's too steep to support itself and it collapses
Explain why an observer can experience two unequal high tides during one day
tidal bulges migrate as the Moon revolves around Earth, so depending on the Moon's position, the tidal bulges may be inclined to the equator, causing an observer to experience two unequal high tides during a day
Contrast flood current and ebb current
tidal currents that advance into the coastal zone as the tide rises are called flood currents, whereas ebb currents are generated by seaward-moving water as the tide falls