Oceans

As glaciers melted at the end of the last Ice Age:

-worldwide sea level increased -estuaries formed -river plains drowned

The average depth of the continental shelf is approximately:

200 meters

Coastal erosion

Erosion occurs in interesting patterns along coastlines. Where the earth's oceans and land masses meet, both rivers and ocean currents influence sediment transport and depositions. For example, waves build coastal beaches by depositing both seaweed and sand. The seaweed helps to keep the sand in place on beaches. When seaweed is removed, sand is also removed by those same ocean waves. Sand brought to the ocean by rivers form either deltas or sandbars. Delta sand piles up until it chokes the original channel of the river. The river then finds a new place to flow and builds up a new delta. If the river breaks into several branches, each branch is called a distributary. Rivers that flow long distances across plains before reaching the sea bring only fine sand, silt, and clay into the ocean. Coasts that are open to large storms and strong currents are places from which sediment is swept away and redeposited elsewhere. The world's largest river, the Amazon, contributes its load of sand and silt to ocean floor deposits instead of building a great delta. As ocean waves move sand, silt, and clay, the smaller particles are separated from the larger grains and are redeposited in separate places. The white beach sand we are accoustom to is composed of quartz, gypsum, and calcium carbonate, but basaltic lavas can be broken into black sand, which makes black sand beaches on some islands.

turbity currents

From the top of the continental slope, a steady current of silt-laden water keeps moving downhill because the silt-water weighs more than ocean water and settles to the bottom. In addition to this constant flow, mild earthquakes set free great clouds of mud and sand called turbidity currents. These currents cover hundreds of square miles of abyssal plain with graded beds of sediment. Medium-sized grains of sand settle at the bottom of each deposit, finer sand settles in the middle, and the top is covered by silt. In 1929 near the Grand Banks of Newfoundland, one turbidity current went down the continental slope at 100 kilometers per hour. The speed of this turbidity current was measured using the time between the snapping of one telegraph cable to the snapping of the next cable. The deposit made by this turbidity current was over a meter thick, many kilometers beyond the bottom of the continental slope, and covered an area of about 250,000 square kilometers.

How limestone rock is formed:

In shallow parts of the ocean, calcite (calcium carbonate) from shells of microscopic animals called foraminifera, seashells, and fragments of seashells broken by the waves accumulates. These deposits slowly accumulate and eventually form limestone rock.

Erosion Features in Oceans

In shallow, clear, tropical ocean waters, bioherms build up. Bioherms consist of algae, corals, tiny needles of sponges, shells, and fragments of shells broken by the waves. A modern bioherm currently growing in place is composed of corals and coralline algae built upon other similar organic structures and is called a reef. Bioherms are found in many places - sometimes along the coast, sometimes parallel to the coast but miles away, and sometimes circling a volcanic island. Coral reefs surrounding a volcanic island are called atolls. Some volcanic islands have been cut off by waves and submerged, in which case they are called guyotes. The tops of many guyotes are as far as a kilometer under the surface of the ocean, indicating either that the sea has risen at least that far, or that hundreds of volcanoes have sunk. Reefs and bioherms are good places to look for petroleum. Oil companies hire geologists to locate bioherms, some of which are now part of the sedimentary rocks covering a continent. Buried coral atolls are found in Canada and under downtown Chicago.

The Groundwater Erosion Process:

In valleys, groundwater is often pushed forward or toward the surface due to pressure from rainwater that falls on the nearby highlands and seeps into the ground. If the water table reaches the surface, a lake, a river, or a spring is formed. A spring formed in a desert biome is surrounded by plants that take advantage of the water supply, forming an oasis. Water which is now coming to the surface at oases in the Sahara Desert came from rain that fell on hills near the desert during the Middle Ages - 800 to 1,000 years ago. When carbonic acid enters limestone, it dissolves the limestone as it flows along joints and forms underground streams. This erosion eventually produces a cavity by an underground stream known as a cavern. Water dripping from the roof of caverns loses its carbonic acid through evaporation of carbon dioxide. Lime (a grayish-white substance extracted from the limestone), no longer held in solution is deposited as stony icicles and pillars called stalactites and stalagmites.

What does sand grab onto to help form beaches?

Seaweed

The Lake Cycle

Sections of rivers blocked by landslides, by debris, or by dams are called lakes. Lake basins fill with gravel, sand, and mud. They turn into bogs and, later, into solid ground. Lakes commonly fill with layers of differently colored materials in summer and winter, or after storms and during quiet periods following storms. These layers, called varves, include sand brought in by streams in spring and summer, and smaller particles of clay that slowly settle when the water is quiet. The layers making up the varves may be thin or thick depending upon the way it was formed.

What causes the increased salinity of lagoon water?

The shallow depths increases the rate of evaporation

Groundwater Erosion

Water is found in all soil. Rainwater filters down until it reaches a zone saturated with water. The top of this water-saturated zone is called the water table. Wells must enter the water table. There, the well will fill with water that can be pumped out. If water is pumped out faster than it is replaced, the water table will lower until it is too low to be pumped. Then the wells must be deepened.

Groundwater refers to which of the following?

Water the has been absorbed into the ground to form the water table

Estuaries

When continental glaciers covered northern North America and Europe, the sea was 200 meters shallower than it is at present. River valleys extended out onto the continental shelf, where the ocean is now up to 200 meters deep. The wide mouths of rivers, like the Potomac, were valleys made by erosion. As the glaciers melted the oceans filled and drowned these river valleys, which are now called estuaries. The salinity of water in an estuary fluctuates as marine tidal waters move in and out.

How oceans are formed

When waves splash against a cliff they accomplish mechanical weathering as well as erosion. Air is compressed in the cracks of rocks and breaks off boulders that fall to the bottom of the cliff. The separated rocks are hurled against each other by the waves and further broken. Smaller pieces are transported along the beach by waves, producing beach slopes covered by cobbles. In the sea, corners and edges are smoothed by mechanical erosion. Stones eventually become quite rounded. Smaller fragments are broken into sand which is left on a beach. In many places, sand is piled up on the beach by ordinary high tides, but is rapidly removed by large storm waves.

Costaline

Where a coastline is fringed by shallow deposits, such as a reef, bioherm, sandbar, or sand island, the waters behind the barrier form a special type of environment called a lagoon. In a lagoon water that comes over the barrier or through gaps in the barrier replaces water that is rapidly evaporating from the shallows. In some cases the inflowing and evaporation leaves the water of the lagoon much saltier than the water in the ocean.

Ocean depositions

Where the ocean is over a mile deep, cold temperatures and pressure keep carbon dioxide dissolved. Here, the bacteria abundant in sea-bottom mud add more carbon dioxide as they reprocess dead organic material back into plant nutrients. Entire skeletons of fish and whales are dissolved in the carbonic acid at the bottom of the ocean. Closer to the shore, ocean deposits are made of mud and sand from the land, and of seashells and reefs from the ocean. Along most coasts the sea becomes deeper very gradually for dozens or hundreds of kilometers, reaching an average depth of about 200 meters above the continental shelf. The sea then becomes hundreds of meters deeper for each kilometer of the continental slope until the ocean bottom is reached at the depth of four kilometers or more.

Bioherms are made of:

algae, corals and shells

A reef that surrounds a volcanic island is a(n):

atoll

A turbidity current is an underwater:

avalanche

One characteristic of a lagoon is often:

concentrated salt

Lake Cycle:

river blockage, plain flooding, sediment deposition, bog formation, solid ground

The original source of all sand is:

rocks

Rivers that flow long distances deposit __________ into the ocean.

sand and silt