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From Wikipedia, the free encyclopedia

Soil with broken rock fragments overlying bedrock, Sandside Bay, Caithness
Soil with broken rock fragments overlying bedrock, Sandside Bay, Caithness

In geology, bedrock is the lithified rock that lies under a loose softer material called regolith at the surface of the Earth or other terrestrial planets. The broken and weathered regolith includes soil and subsoil. The surface of the bedrock beneath the soil cover is known as rockhead in engineering geology,[1][2] and its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits (also known as drift) can be extremely thick, such that the bedrock lies hundreds of meters below the surface.[3]

Bedrock may also experience subsurface weathering at its upper boundary, forming saprolite.

A solid geologic map of an area will usually show the distribution of differing bedrock types, rock that would be exposed at the surface if all soil or other superficial deposits were removed.[4]

Soil profile with bedrock labeled R
Soil profile with bedrock labeled R

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Transcription

When it comes to planet Earth there are various layers between the surface and the core. Buried just beneath the Earth's surface, beneath roots and soil, is the solid bedrock of Earth's crust. Bedrock often serves as the parent material for soil, which is an essential ingredient for most organisms that live on land. Air and water can penetrate the rock through cracks and fissures, chemically breaking it up and ultimately creating soil. This weathering of bedrock is so fundamental to life on Earth that scientists have dubbed the layer where weathering happens the, "critical zone". But we know very little about the mechanisms that control the thickness of this zone where rock, air, and water interact. Fracturing of rock also controls how mountain ranges erode away. Now, scientists have found a way to predict the depth and extent of bedrock weathering, given a location's topography. The group developed a model that estimates the thickness of the layer where the bedrock is broken up or fractured, given the forces generated by topography, gravity and plate tectonics. The model computes how topography focuses gravitational forces due to the weight of overlying rock, and regional forces associated with the push or pull of tectonic plates. It takes these forces into account to determine whether and to what extent bedrock will crack under the pressure associated with a given landscape's topography. Using their model, they found that if a landscape is undergoing little tectonic compression, the fractured zone should parallel the overlying topography (think layers of lasagna). If , however, a region is under high tectonic compression, the fractured zone will resemble a mirror image of the landscape: thicker beneath ridges and thinner under valleys. To test the models predictions the researchers visited three sites within the United States with varying tectonic forces. In each location, they took seismic and electrical conductivity measurements to gauge the extent of the fracturing in the underlying bedrock. The speed at which seismic waves move through rock can provide data on the mechanical state of the rock. For example, seismic waves move faster through solid rock and slower through rock containing many fractures. Ultimately, their measurements matched well with their model's predictions. This model could be used to gain more knowledge about the mechanical properties of bedrock and understand how Earth's critical zone functions. The model may also help gauge a building site's susceptibility to earthquake shaking or landslides.

Contents

In soil science

Soil scientists use the capital letters O, A, B, C, and E to identify the master soil horizons. Hard bedrock, which is not soil, uses the letter R.

See also

References

  1. ^ Price, David George, Engineering Geology: Principles and Practice, Springer, 2009, p. 16 ISBN 978-3540292494
  2. ^ Gribble C. & McLean A. (2003). Geology for Civil Engineers. CRC Press. p. 113. ISBN 9780203362150.
  3. ^ "Swinford, E. Mac What the glaciers left behind – drift thickness map of Ohio, Ohio Department of Natural Resources, Division of Geological Survey, newsletter 2004, No.1" (PDF). Archived from the original (PDF) on 2012-10-02. Retrieved 2012-09-12.
  4. ^ BGS. "Digital Geology – Bedrock geology theme". Archived from the original on 13 December 2009. Retrieved 2009-11-12.

External links

This page was last edited on 10 December 2018, at 16:22
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