Why don't these mountains look the same?
The same plate tectonics processes caused both sets of mountains to rise. In both cases, two continental plates smashed together at a convergent plate boundary. The Himalaya Mountains on the left are still uplifting. The landscape is steep and rugged. The photo on the right shows the Appalachian Mountains. These mountains were once steep like the Himalaya. If the only processes on Earth were plate tectonics processes, the Appalachians might still look like the Himalaya. But the Appalachian Mountains are low and rounded. Over time the Appalachians have undergone weathering and erosion. This chapter is about the processes that modify the landscape. These processes alter landforms. Some of these processes create new landforms.
The weathering of rocks and minerals can be mechanical or chemical. Mechanical weathering changes the size of a mineral or rock. Mechanical weathering does not change the chemical composition of that material. Chemical weathering changes the composition of a mineral or rock. Different types of weathering can alter the same material. Soil forms on top of rock. The type of soil that forms depends on the environment of the region. For example, warm and wet climates form different soils than cold and dry climates. A profile through the soil shows different horizons. Topsoil is the most important layer for crops. Water, ice, wind, and gravity create or modify landforms on Earth's surface. These agents can erode or deposit features that indicate their presence. Erosion by water and ice lowered and rounded the Appalachians. These old mountains no longer look like the Himalaya. Someday the Himalaya may look like the Appalachians do now.