My alluvial island is formed primarily from silt. The barrier of silt is being washed away from the delta!
It is more accurate to say it is formed from clay and silt.
Silt is formed when fine particles of rock and mineral are carried by water and deposited in layers. Factors that contribute to silt formation include erosion of rocks, weathering, and the movement of water.
A delta.
delta
Over time the silt changes the shape of the river as it is formed into islands, sandbars, and river bends
Small particles of sand, silt, and clay
Shale
a delta
It is formed from the silt, sand and small rocks that flow downstream in the river and are deposited in the delta.
Delta
They are formed when water from rain or snow melt leaves mountain valleys and fans out the silt it carries with it.