How do water and air cause rocks to crumble?
http://www.edu.pe.ca/southernkings/weatheringjm.htm
http://education.nationalgeographic.com/education/encyclopedia/weathering/?ar_a=1
Rocks expand and contract when they are heated and cooled, which can cause them to break.
Water and air can cause rocks to crumble through a process called weathering. Weathering is the mechanical, chemical, and biological process by which rocks break down and disintegrate over time.
To understand how water and air cause rocks to crumble, let's break it down into two main types of weathering: physical weathering and chemical weathering.
1. Physical Weathering: Water and air play a significant role in physical weathering. Here's how it happens:
- Water: Water can enter cracks and crevices in rocks. When this water freezes and expands, it exerts pressure on the surrounding rock, causing the crack to widen. This process, known as frost wedging, can repeat numerous times, ultimately breaking the rock apart.
- Air: The air contains a variety of gases, including oxygen and carbon dioxide. Oxygen molecules can react with certain minerals within rocks, causing them to weaken and break. Additionally, air can carry small particles, such as sand or dust, which can act as abrasives and physically erode the surface of rocks over time.
2. Chemical Weathering: Water and air also contribute to chemical weathering, which involves the chemical alteration of rocks. Here's how it occurs:
- Water: Water can carry dissolved substances, such as acids or salts, which can react with minerals present in rocks. For instance, when rainwater combines with carbon dioxide in the atmosphere, it forms a weak carbonic acid. This acid can dissolve minerals like calcite in limestone rocks, leading to their decomposition and crumbly texture.
- Air: Gases in the air, like sulfur dioxide or nitrogen oxides produced by industrial activities or natural sources, can combine with rainwater to form acid rain. Acid rain contains strong acids that can chemically break down rocks, accelerating their weathering process.
Overall, water and air cause rocks to crumble through a combination of physical and chemical weathering processes. These processes gradually weaken the structural integrity of rocks, leading to their eventual disintegration.