Siblings Anthony and Zola visit the same beach each summer. They measure the length of the sandbar at low tide every year. They notice that each year it gets one meter narrower. What is the cause of this phenomenon?

Erosion wears away and carries off sand and other sediment. If the sandbar loses about one meter of width each year, it is being worn away, so erosion is the cause. Plate tectonics and the water cycle do not directly explain the sandbar becoming narrower in this way.

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