The element of nature that can cause mechanical weathering by flowing over rocks or carrying along in a current is water.

Here's how it works:

* Abrasion: Water, especially when it's moving quickly in a river or ocean current, carries sediment like sand and pebbles. This sediment acts like sandpaper, grinding against rocks and gradually wearing them down.

* Hydraulic Action: The force of moving water can exert pressure on rock surfaces, especially in cracks and crevices. This pressure can cause the rock to break apart.

* Freeze-Thaw: Water expands when it freezes. If water seeps into cracks in rocks and then freezes, the expanding ice can put enough pressure on the rock to cause it to break. This is a common form of mechanical weathering in cold climates.

So, water, through its various actions, is a powerful force in shaping the Earth's surface through mechanical weathering.