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Geology of the National Parks


Forces in the Earth: Plate Tectonics

Disrupted thick sandstone beds on west side Mt Olympus
Fig. 23. Highly disrupted thick sandstone beds in slate on the west side of Mount Olympus

Geologists have long sought an explanation for how sedimentary rocks derived from flat-lying sediments in the sea could be so folded and compressed and how they have been raised above the sea. It is now obvious that different crustal blocks have moved toward each other, crushing and compressing strata caught between them; it is not so obvious why these blocks moved. In recent years, scientists using sophisticated electronic devices have learned much about the physical properties of the earth, such as its magnetic, gravitational, and heat-flow properties. Much of this information has been gathered from the oceans. Sediments and rocks from the ocean floor can now be sampled by drilling, and the exact ages of many rocks can be determined by measuring their radioactive elements. These new data from the ocean floor and the details of rock structure on the land have been unified in the theory of plate tectonics.

Material in this site has been adapted from Guide to the Geology of Olympic National Park by Rowland W. Tabor, of the USGS. It is published by The Northwest Interpretive Association, Seattle.

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