What are alluvial deposits primarily made up of?

Alluvial deposits are primarily made up of sands and gravels. These sediments are typically formed from the erosion and transportation of materials by water, particularly in river and floodplain environments. As water flows, it picks up various materials and deposits them in downstream locations where the flow velocity decreases, allowing for coarser materials like sand and gravel to settle.

In alluvial environments, the composition can vary based on the geological features of the surrounding area and the hydrological characteristics of the watercourse. However, the defining characteristic is that alluvial deposits are formed from materials that have been weathered and transported by water, leading to sediments that are predominantly sandy and gravelly in nature. This is in contrast to other soil types or materials that might be found in different settings, such as clay and silt, which are typically associated with finer-grained deposits found in still water environments like lakes or estuaries.