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.
Land formed by silt deposited by a river is called a delta.
Over time the silt changes the shape of the river as it is formed into islands, sandbars, and river bends
A delta.
delta
Small particles of sand, silt, and clay
abyssal plains
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