Geomorphic Processes

Desertification is the process by which fertile land becomes desert, typically as a result of drought, deforestation, or inappropriate agriculture. Defertilization is not a standard term for this process, and barren land is a state rather than a process.

Erosion is the geological process in which earth materials are worn away and transported by natural forces such as wind, water, ice, or gravity. In contrast, weathering is the static breaking down of rocks, while oxidation is a specific chemical reaction. Because the question specifies the removal and transport of particles, erosion is the correct term.

Acid rain is a classic example of chemical weathering because it involves a chemical reaction between acidic water and minerals in rocks, causing them to dissolve or alter. Freezing, thawing, and pressure are physical processes that mechanically break rocks apart without changing their chemical composition. Therefore, acid rain is the only chemical process listed.

Freezing and thawing (frost wedging) physically breaks rocks apart without changing their chemical composition, making it a mechanical weathering agent. Carbon dioxide, acid rain, and oxygen cause chemical weathering by reacting with minerals in the rock.

Sediment consists of solid material, such as minerals and organic debris, that is transported and deposited by water or wind. Soil and rocks are broader terms, and the Mekong is a river.

While silt is sometimes described as fine sand, it is actually fine granular material between sand and clay in size. It is composed of mineral particles that are larger than clay but smaller than sand, commonly found in river deposits and fertile soil.

Dikes are typically used to control or prevent flooding by holding back water, not to direct the flow of sand. They are barriers against water, not sand management tools.

A delta is a landform created by the deposition of sediment that is carried by a river as the flow leaves its mouth and enters slower-moving or stagnant water.

In the hydrologic cycle, transport refers to the movement of water from one location to another, such as through atmospheric currents or surface runoff.

Mineralization is the process where organic material is replaced by minerals, turning it into a fossil. Sedimentation is the deposition of material, but not the specific process of turning into stone.

A geologic era is a large span of time in the geologic time scale, typically characterized by major changes in life forms and sediment deposition.

Erosion is minimized when the ground is flat and covered by vegetation. Vegetation roots anchor the soil, while flat terrain reduces the speed of water runoff.

The Himalaya were formed by the collision of the Indian tectonic plate with the Eurasian plate, a process known as plate tectonics.

A delta is a landform created by the deposition of sediment that is carried by a river as the flow leaves its mouth and enters slower-moving water.

An alluvial plain is a flat area of land next to a river, formed by the deposition of sediment (alluvium) carried by the river during flooding.