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Geography (from Greek γεωγραφία - geografia) is the study of the Earth and its lands, features, inhabitants, and phenomena. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes (276-194 B.C.). Four historical traditions in geographical research are the spatial analysis of natural and human phenomena (geography as a study of distribution), area studies (places and regions), study of man-land relationship, and research in earth sciences. Nonetheless, modern geography is an all-encompassing discipline that foremost seeks to understand the Earth and all of its human and natural complexities-- not merely where objects are, but how they have changed and come to be. As "the bridge between the human and physical sciences," geography is divided into two main branches - human geography and physical geography.

Wednesday, February 18, 2009

The Rock Cycle

“Rocks are continually formed, modified, destroyed and reconstructed as part of the rock cycle. They are formed and modified by endogenic (internal) forces; they are destroyed by exogenic (external) forces of erosion on exposure to weather and climate; they are reconstituted by the deposition of sediments.”
For this statement students need to have a knowledge of the basic rock classification of igneous, sedimentary and metamorphic. They should be able to give both Irish and world examples of each rock type.

Igneous rocks
Igneous rocks are usually divided into two groups-intrusive (plutonic) and extrusive (volcanic) rocks. Granite is the most common of the intrusive rocks and it underlies most of the continents. Basalt is the most common of the extrusive rocks and it underlies most of the oceans. Granite was formed when magma intruded into the earth’s crust. This cooled slowly over a long period of time and formed a coarse grained rock that is very resistant to erosion. You need to know about the colour, the constituent minerals and the uses of granite. Major locations in Ireland include the Mournes and the Dublin-Wicklow mountains. Basalt was formed when lava was exposed at the surface and cooled quickly. It is a fine-grained, dull coloured rock and it is noted for its resistance (hardness). Sometimes, if it cools rapidly, it can split into hexagonal columns. The Giant’s Causeway is a good example of this. Basalt often results in the formation of a plateau---good examples are the Antrim-Derry Plateau and the Deccan of India.

Sedimentary Rocks
These rocks are formed by compressed sediments or fragments and often form on lakebeds or under the sea. There are three basic categories of sedimentary rocks. Students should know how each type are formed and be able to give examples of each. Sedimentary rocks form in layers (bedding planes). The three groups of sedimentary rocks are:
Organic sedimentary rocks - these are formed from the compacted remains of living things. Limestone and Peat are obvious examples. Ireland’s limestone was formed under the sea and covers large areas of the country. However, much of this is covered by glacial till (see glaciation) but is exposed in areas such as the Burren in Co. Clare. Limestone is also very evident in areas such as the Karst region of Croatia.
Inorganic (Mechanical) sedimentary rock - these are formed from the compacted remains of the broken down particles of other rocks; Sandstone and Shale are examples. Sandstone is the second most common rock found in Ireland and can be found in the Magillicuddy Reeks, Co. Kerry.
Chemically Derived sedimentary rocks - these include gypsum and rock salt. Gypsum is found in Co.Cavan. However, the most prized deposits associated with chemical deposition are oil and gas. Significant deposits of gas have been found off both the south and west coasts of Ireland.

Metamorphic Rocks
Metamorphic rocks are rocks that have been changed due to great heat and/or pressure. They were originally either igneous or sedimentary. This change is due to either igneous activity, where great heat changes the original rock on contact or to tectonic activity, where converging plates generate heat and pressure thus causing rocks to change their state. Typical examples of metamorphic rocks include-Quartzite (from sandstone) and Marble (from limestone).This section also requires students to be familiar with the rock cycle. In other words, they should have both Irish and international information with regard to one of the following: mining; oil/gas exploration extraction of building materials; geothermal energy production.

Click the link below to have a look at an animation of the Rock Cycle

Below is a video about rocks and the rock cycle

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