What is the introduction about alluvial islands?

Alluvial Island: It is located at the outlet of a large river or outside the plain coast. It is a new land formed by the accumulation of river sediment or sea currents. The world's largest alluvial island, Marajó Island, is an island at the mouth of the Amazon River, the world's largest river. It covers an area of ??400,000 square kilometers and is ranked as the 30th largest island in the world. Chongming Island, Changxing Island and the isolated islands in the Yellow River Estuary in my country are all alluvial islands. Sable Island on the east coast of Canada, Cape Tras on the east coast of the United States, and Subi Sand Bar in my country are all sandy beaches formed by ocean currents and wind. Their positions are not fixed, making them dangerous areas for navigation.