influences on weathering

resources from weathering

Some resources are concentrated by weathering processes. In tropical climates, intense chemical weathering carries away all soluble minerals, leaving behind just the least soluble components. The aluminum oxide, bauxite, forms this way and is our main source of aluminum ore.



A regions climate strongly influences weathering. Climate is determined by the temperature of a region plus the amount of precipitation it receives. Climate is weather averaged over a long period of time. Chemical weathering increases as: Temperature increases: Chemical reactions proceed more rapidly at higher temperatures. For each 10o C increase in average temperature, the rate of chemical reactions doubles. Precipitation increases: More water allows more chemical reactions. Since water participates in both mechan- ical and chemical weathering, more water strongly increases weathering. So how do different climates influence weathering? A cold, dry climate will produce the lowest rate of weathering. A warm, wet climate will produce the highest rate of weathering. The warmer a climate is, the more types of vegetation it will have and the greater the rate of biological weathering (Figure 1.2). This happens because plants and bacteria grow and multiply faster in warmer temperatures.

rock and mineral type

Different rock types weather at different rates. Certain types of rock are very resistant to weathering. Igneous rocks, especially intrusive igneous rocks such as granite, weather slowly because it is hard for water to penetrate them. Other types of rock, such as limestone, are easily weathered because they dissolve in weak acids. Rocks that resist weathering remain at the surface and form ridges or hills. Shiprock in New Mexico is the throat of a volcano thats left after the rest of the volcano eroded away. The rock thats left behind is magma that cooled relatively slowly and is harder than the rock that had surrounded it. Different minerals also weather at different rates. Some minerals in a rock might completely dissolve in water, but the more resistant minerals remain. In this case, the rocks surface becomes pitted and rough. When a less resistant mineral dissolves, more resistant mineral grains are released from the rock. A beautiful example of this effect is the "Stone Forest" in China, see the video below: The Shiprock formation in northwest New Mexico is the central plug of resistant lava from which the surrounding rock weath- ered and eroded away. Click image to the left or use the URL below. URL:


instructional diagrams

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igneous rocks weather faster than most other rocks because they formed in conditions that are the most different from surface conditions.

a) true

-->  b) false

limestone weathers relatively rapidly because

a) it forms at greater depth and is less stable than rocks that form near the surface.

-->  b) it dissolves in weak acids.

c) it has lots of fractures, which expose it to weathering.

d) none of the above

a rock will weather more quickly in which climate

a) hot and dry

b) cold and wet

c) cold and dry

-->  d) hot and wet

water helps weathering because

a) it increases the temperature.

-->  b) it increases the number of chemical reactions.

c) it increases the amount of oxygen thats available for oxidation.

d) it increases the difference in weathering between different types of minerals.

how is aluminum ore made?

-->  a) intense chemical weathering removes soluble minerals and leaves aluminum oxide.

b) exposed aluminum is oxidized in air.

c) chemical reactions on tree roots concentrate aluminum oxide.

d) aluminum oxide precipitates out of saline water and onto a lake bed.

chemical reactions proceed more rapidly at higher temperatures.

-->  a) true

b) false

climate is determined by

-->  a) temperature

b) precipitation

c) temperature & precipitation

d) none of these

when a less resistant mineral dissolves, more resistant mineral grains are released from rock.

-->  a) true

b) false

precipitation increases both mechanical and chemical weathering.

-->  a) true

b) false

quartz sand is very common on beaches. why might that be?

a) quartz is light so it floats downstream to the beaches more easily.

b) the other minerals are so heavy they fall to the bottom of a stream and dont make it to the beach.

-->  c) quartz is resistant to weathering so it is left after the other minerals are gone.

d) quartz is easily weathered so it is weathered out and transported to the beach.

diagram questions

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