MOUNTAINS

CONCEPT

Among the most striking of geologic features are mountains, created by several types of tectonic forces, including collisions between continental masses. Mountains have long had an impact on the human psyche, for instance by virtue of their association with the divine in the Greek myths, the Bible, and other religious or cultural traditions. One does not need to be a geologist to know what a mountain is; indeed there is no precise definition of mountain, though in most cases the distinction between a mountain and a hill is fairly obvious. On the other hand, the defining characteristics of a volcano are more apparent. Created by violent tectonic forces, a volcano usually is considered a mountain, and almost certainly is one after it erupts, pouring out molten rock and other substances from deep in the earth.

HOW IT WORKS

Plate Tectonics
Earth is constantly moving, driven by forces beneath its surface. The interior of Earth itself is divided into three major sections: the crust, mantle, and core. The lithosphere is the upper layer of Earth’s interior, including the crust and the brittle portion at the top of the mantle. Tectonism is the deformation of the lithosphere, and the term tectonics refers to the study of this deformation. Most notable among examples of tectonic deformation is mountain building, or orogenesis, discussed later in this essay.

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Northwest’s next big earthquake: Source mapped

This map shows the location of seawater samples taken by scientists and citizen scientists that were analyzed at the Woods Hole Oceanographic Institution for radioactive cesium as part of Our Radioactive Ocean. Cesium-137 is found throughout the Pacific Ocean and was detectable in all samples collected, while cesium-134 (yellow/orange dots), an indicator of contamination from Fukushima, has been observed offshore and in select coastal areas. Credit: Figure by Jessica Drysdale, Woods Hole Oceanographic Institution
This map shows the location of seawater samples taken by scientists and citizen scientists that were analyzed at the Woods Hole Oceanographic Institution for radioactive cesium as part of Our Radioactive Ocean. Cesium-137 is found throughout the Pacific Ocean and was detectable in all samples collected, while cesium-134 (yellow/orange dots), an indicator of contamination from Fukushima, has been observed offshore and in select coastal areas.
Credit: Figure by Jessica Drysdale, Woods Hole Oceanographic Institution

Scientists monitoring the spread of radiation in the ocean from the Fukushima nuclear accident report finding an increased number of sites off the US West Coast showing signs of contamination from Fukushima. This includes the highest detected level to date from a sample collected about 1,600 miles west of San Francisco. The level of radioactive cesium isotopes in the sample, 11 Becquerel’s per cubic meter of seawater (about 264 gallons), is 50 percent higher than other samples collected along the West Coast so far, but is still more than 500 times lower than US government safety limits for drinking water, and well below limits of concern for direct exposure while swimming, boating, or other recreational activities.

Продължете да четете Northwest’s next big earthquake: Source mapped