Helioseismology

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Running head: Water and Island

Water and Island Formations

Daron Hoggatt

University of Oklahoma

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According to the Bible, God created water and then separated the water with dry land. An island or isle is any piece of land that is completely surrounded by water. Water has the chemical formula H2O meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. You can not have an island without water. This essay will line out the determining factors of an islands, continents, and islets. It will also descibe the different types of island formations.

Three quarters of the Earth is covered with water. Water is colorless and comes in more than one form. Water may appear in nature in three states: a liquid, a solid and a gas or vapor. Below freezing, water is a solid, between freezing and boiling it is a liquid, and above its boiling point it becomes a gas. Water changing from a solid to a liquid is said to be melting. When it changes from a liquid to a gas, it is evaporating. Water changing from a gas to a liquid is called condensation.

Let us now look at the five different types of "islands." The five types are: (1) island, (2) islets, (3) continental, (4) river, and (5) volcanic. These are classified by their size and locations among the water.

An island or isle is any piece of land that is completely surrounded by water. Very small islands are called islets. It is also proper to call an emergent land feature on an atoll an islet, since an atoll is a type of island, although this convention is seldom adhered to. A key or cay is another name for a relatively small island or islet.

Continental islands are bodies of land that lie upon the continental shelf of a continent. Examples include Greenland and Sable Island off North America, Barbados and Trinidad off South America, Sicily off Europe, Sumatra and Java off Asia, New

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Guinea and Tasmania off Australia. A special type of Continental Island is the micro continental island, which results when a continent is rifted. The best example is Madagascar off Africa. The Kerguelen Islands and some of the Seychelles are also examples. Another subtype is the barrier island: an accumulation of sand on the continental shelf.

River islands occur in river deltas and in large rivers. They are caused by deposition of sediment at points in the flow where the current loses some of its carrying capacity. In essence, they are river bars, isolated in the stream. While some are ephemeral, and may disappear if the river's water volume or speed changes, others are stable and long-lived.

Volcanic islands are built by volcanoes. Mid-ocean examples are not part of any continent. One type of volcanic island is found in a volcanic island arc. These islands arise from volcanoes where the seduction of one plate under another is occurring. Examples include the Mariana Islands, the Aleutian Islands, Republic of Mauritius and most of Tonga in the Pacific Ocean. Some of the Lesser Antilles and the South Sandwich Islands are the only Atlantic Ocean examples.

Another type of volcanic island occurs where an oceanic rift reaches the surface. There are two examples: Iceland, which is the world's largest volcanic island, and Jan Mayen--both are in the Atlantic.

A third type of volcanic island is those formed over volcanic hotspots. A hotspot is more or less stationary relative to the moving tectonic plate above it, so a chain of islands results as the plate drifts. Over long periods of time, this type of island is

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eventually eroded down and "drowned" by isostatic adjustment, becoming a seamount. Plate movement across a hot-spot produces a line of islands oriented in the direction of the plate movement. An example is the Hawaiian Islands, from Hawaii to Kure, which then extends beneath the sea surface in a more northerly direction as the Emperor Seamounts. Another chain with similar orientation is the Tuamotu Archipelago; its older, northerly trend is the Line Islands. The southernmost chain is the Austral Islands, with its northerly trending part the atolls in the nation of Tuvalu. Tristan da Cunha is an example of a hotspot volcano in the Atlantic Ocean. Another hot spot in the Atlantic is the island of Surtsey, which was formed in 1963.

An atoll is an island formed from a coral reef that has grown on an eroded and submerged volcanic island. The reef rises to the surface of the water and forms a new island. Atolls are typically ring-shaped with a central lagoon. Examples include the Maldives in the Indian Ocean and Line Islands in the Pacific.

How are islands formed? "Although there are a number of way in which islands are formed, all islands are either continental or oceanic. Oceanic islands are formed in the ocean, while continental islands are formed as they break away from larger landmasses.

Plate tectonics, or the movement of different sections of the earth's crust, play a significant role in the creation of islands. Islands can form by separating plate movement, the collision of plates, or when plates move over "hot spots" of volcanic activity."

Exactly what causes plate tectonics is not known. One theory is that heat within the Earth's mantle pushes the plates. Another theory is that gravity is pulling the older, colder, and much heavier ocean floor with more force than the newer, lighter seafloor.

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Whatever ever drives the movement, activity has four types of boundaries: divergent boundaries, where new crust is formed; convergent boundaries, where crust is consumed; collisional boundaries, where two land masses collide; and transform boundaries, where two plates slide against each other.

In the 1960s, geologists were looking for ways to prove or disprove the new idea of moving plates. Exploration of magnetic anomalies at mid-ocean ridges provided strong

support for the seafloor spreading. Geologists studied other ocean features to see how

they

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