Here's how:

* Erosion: Beaches are constantly being eroded by waves, currents, and wind. These forces carry away sand and other materials, making the beach smaller. This is erosion.

* Deposition: The sand and other materials eroded from the beach can be transported and deposited elsewhere, sometimes building up new beaches or sandbars. This is deposition.

So, a beach can be both eroding and depositing at the same time. For example, a strong wave might erode sand from one part of a beach and deposit it further down the shore.

It's important to understand that both erosion and deposition are natural processes that shape beaches and coastlines. However, human activities can sometimes accelerate erosion or disrupt natural deposition patterns, leading to problems like coastal erosion.