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Weathering and Topography Help

By — McGraw-Hill Professional
Updated on Sep 4, 2011

Introduction to Weathering and Topography

Nothing lasts forever. This applies to winning sports teams as well as rock; the stuff of the Earth. The keys are timing and environment. Athletes do great for years, but sooner or later, they experience an injury or age catches up with them and they aren’t able to maintain earlier levels of performance. This is true of any activity.

Aging and change over time are constants in nature. Whether something ages in a few months like cheese, years like wine, or centuries like monuments and old buildings, nothing stays the same forever.

Rocks and landforms are no exception. They are eventually worn away over time. As diverse as the world’s environment is, so too are the many ways that rocks can be worn away. Time is the key factor. Some rock surfaces are changed over decades, while some take millions of years. Rock destruction occurs during everything from landslides to acid rain. We will look at these different rock altering mechanisms and see which ones humankind impacts, compared to those in Mother Nature’s tool kit.

Denudation

Most people use the word, weathering , as an overall term, but it actually comes under a larger category called denudation . Denudation takes place when surface layers are removed from underlying rock. They are laid bare. When the wind blows constantly on a high mountain slope, there is hardly any soil left on the bare surfaces except for grains that fall into protected cracks and fissures. This is especially obvious in rock outcrops where very little soil gathers.

Denudation takes place when rock disintegrates and is removed from the surface of continents.

Denudation is an umbrella word covering three main types of rock change and removal. These are weathering , mass wasting , and erosion . All three have the same end product, movement of rock, but they make it happen in different ways. These processes are compared below.

  • Weathering takes place when rocks are broken down and transformed at or near the surface by atmospheric and biological agents. Weathering wears away and chemically changes rocks, but there is hardly any rock movement.
  • Mass wasting is more active than weathering. It happens when there is a downward shift of broken rock material down slope due to gravity’s pull. Mass wasting or rock shift can also cause loose rock to suddenly move over short distances, like during a rock slide.
  • Erosion is a bit like mass wasting, but covers rock transport over much greater distances and is helped along by wind and/or water. Erosion causes sediments to travel over great distances, like from continental land masses to the ocean bottom.

Often, denudation takes place in a step-wise manner. First, denudation starts with weathering. Any loosened rock material is then affected by gravity, so we see the following equation that ends with mass wasting.

Weathering + Gravity → Mass wasting

If a free-flowing stream or constant wind is added to mass wasting, then erosion takes place and becomes the product of the equation.

Weathering + Gravity + Moving fluid → Erosion

Mass wasting and erosion, then, sometimes overlap. They can also include some type of flow, like a mudflow.

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