How does weathering affect mountains

Weathering is the process that changes solid rock into sediments. With weathering, rock is disintegrated into smaller pieces. The four forces of erosion are water, wind, glaciers, and gravity.

Water is responsible for most erosion. Water can move most sizes of sediments, depending on the strength of the force. Wind moves sand-sized and smaller pieces of rock through the air. Glaciers move all sizes of sediments, from extremely large boulders to the tiniest fragments. Gravity moves broken pieces of rock, large or small, down slope.

These forces of erosion will be covered later. While plate tectonics forces work to build huge mountains and other landscapes, the forces of weathering and mass wasting gradually wear those rocks and landscapes away, called denudation. Together with erosion, tall mountains turn into hills and even plains.

No human being can watch for millions of years as mountains are built, nor can anyone watch as those same mountains gradually are worn away. But imagine a new sidewalk or road. The new road is smooth and even. Over hundreds of years, it will completely disappear, but what happens over one year? What changes would you see? What forces of weathering wear down that road, or rocks or mountains over time?

Mechanical weathering , also called physical weathering, breaks rock into smaller pieces. These smaller pieces are just like the bigger rock, just smaller.

That means the rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock. There are many ways that rocks can be broken apart into smaller pieces.

Ice wedging , also called freeze-thaw weathering , is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point. Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons. Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside called talus.

Abrasion is another form of mechanical weathering. In abrasion, one rock bumps against another rock. Now that you know what mechanical weathering is, can you think of other ways it could happen?

Without weathering, geologic features would build up but would be less likely to break down. Weathering is the process that changes solid rock into sediments. Sediments were described in the Rocks chapter. With weathering, rock is disintegrated. It breaks into pieces. Once these sediments are separated from the rocks, erosion is the process that moves the sediments.

The four forces of erosion are water, wind, glaciers, and gravity. Figure 1. A once smooth road surface has cracks and fractures, plus a large pothole. While plate tectonics forces work to build huge mountains and other landscapes, the forces of weathering gradually wear those rocks and landscapes away. Together with erosion, tall mountains turn into hills and even plains. No human being can watch for millions of years as mountains are built, nor can anyone watch as those same mountains gradually are worn away.

But imagine a new sidewalk or road. The new road is smooth and even. Over hundreds of years, it will completely disappear, but what happens over one year? What changes would you see figure 1? What forces of weathering wear down that road, or rocks or mountains over time? Follow this link to view some animations of different types of weathering processes.

Mechanical weathering also called physical weathering breaks rock into smaller pieces. These smaller pieces are just like the bigger rock, just smaller.

That means the rock has changed physically without changing its composition. The smaller pieces have the same minerals, in just the same proportions as the original rock. There are many ways that rocks can be broken apart into smaller pieces. Ice wedging is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point figure 2. Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons.

Ice wedging breaks apart so much rock that large piles of broken rock are seen at the base of a hillside, as rock fragments separate and tumble down. Abrasion is another form of mechanical weathering. In abrasion, one rock bumps against another rock. Figure 3. Rocks on a beach are worn down by abrasion as passing waves cause them to strike each other. Abrasion makes rocks with sharp or jagged edges smooth and round.

If you have ever collected beach glass or cobbles from a stream, you have witnessed the work of abrasion figure 3. Now that you know what mechanical weathering is, can you think of other ways it could happen? Plants and animals can do the work of mechanical weathering figure 4. Burrowing animals can also break apart rock as they dig for food or to make living spaces for themselves. Figure 4. Mechanical weathering increases the rate of chemical weathering.

As rock breaks into smaller pieces, the surface area of the pieces increases figure 5. With more surfaces exposed, there are more surfaces on which chemical weathering can occur. Figure 5. Mechanical weathering may increase the rate of chemical weathering. Chemical weathering is the other important type of weathering.

The underlying rocks, released from overlying pressure, can then expand. As the rock surface expands, it becomes vulnerable to fracturing in a process called sheeting. Another type of mechanical weathering occurs when clay or other materials near rock absorb water. Clay, more porous than rock, can swell with water, weathering the surrounding, harder rock. Salt also works to weather rock in a process called haloclasty. Saltwater sometimes gets into the cracks and pores of rock.

If the saltwater evaporate s, salt crystals are left behind. As the crystal s grow, they put pressure on the rock, slowly breaking it apart. Honeycomb weathering is associated with haloclasty. As its name implies, honeycomb weathering describes rock formations with hundreds or even thousands of pits formed by the growth of salt crystals.

Honeycomb weathering is common in coastal areas, where sea sprays constantly force rocks to interact with salts. Haloclasty is not limited to coastal landscapes. Salt upwelling , the geologic process in which underground salt dome s expand, can contribute to weathering of the overlying rock. Structures in the ancient city of Petra, Jordan, were made unstable and often collapsed due to salt upwelling from the ground below.

Plants and animals can be agents of mechanical weathering. The seed of a tree may sprout in soil that has collected in a cracked rock. As the root s grow, they widen the cracks, eventually breaking the rock into pieces.

Over time, trees can break apart even large rocks. Even small plants, such as mosses, can enlarge tiny cracks as they grow. Animals that tunnel underground, such as moles and prairie dogs, also work to break apart rock and soil.

Other animals dig and trample rock aboveground, causing rock to slowly crumble. Chemical weathering changes the molecular structure of rocks and soil. For instance, carbon dioxide from the air or soil sometimes combines with water in a process called carbonation.

This produces a weak acid, called carbonic acid , that can dissolve rock. Carbonic acid is especially effective at dissolving limestone. When carbonic acid seeps through limestone underground, it can open up huge cracks or hollow out vast networks of cave s. Carlsbad Caverns National Park, in the U. The largest is called the Big Room. With an area of about 33, square meters , square feet , the Big Room is the size of six football fields.

Sometimes, chemical weathering dissolves large portions of limestone or other rock on the surface of the Earth to form a landscape called karst. In these areas, the surface rock is pockmarked with holes, sinkhole s, and caves.

Hundreds of slender, sharp towers of weathered limestone rise from the landscape. Another type of chemical weathering works on rocks that contain iron. These rocks turn to rust in a process called oxidation. Rust is a compound created by the interaction of oxygen and iron in the presence of water. As rust expands, it weakens rock and helps break it apart. Hydration is a form of chemical weathering in which the chemical bond s of the mineral are changed as it interacts with water.

One instance of hydration occurs as the mineral anhydrite reacts with groundwater. The water transforms anhydrite into gypsum , one of the most common minerals on Earth.

Another familiar form of chemical weathering is hydrolysis. In the process of hydrolysis, a new solution a mixture of two or more substances is formed as chemicals in rock interact with water.

In many rocks, for example, sodium minerals interact with water to form a saltwater solution. Hydration and hydrolysis contribute to flared slope s, another dramatic example of a landscape formed by weathering and erosion. Living or once-living organisms can also be agents of chemical weathering. The decay ing remains of plants and some fungi form carbonic acid, which can weaken and dissolve rock.

Some bacteria can weather rock in order to access nutrient s such as magnesium or potassium. Clay minerals, including quartz , are among the most common byproduct s of chemical weathering. For example, certain kinds of air pollution increase the rate of weathering. Burning coal , natural gas , and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere.

When these chemicals combine with sunlight and moisture, they change into acids. They then fall back to Earth as acid rain. Acid rain rapidly weathers limestone, marble , and other kinds of stone. The effects of acid rain can often be seen on gravestone s, making names and other inscription s impossible to read. Acid rain has also damaged many historic buildings and monument s. It was carved 1, years ago and sat unharmed for centuries.