Sunken Sub

The captain of a submarine tries at all costs to avoid letting his sub come to rest on a clay or sandy ocean bottom. He knows that if this happens, it can be fatal. Why?

Water pressure pushes perpendicular to a submarine's hull at every point, at the bottom as well as at the top and sides. When a sub settles on a clay or sandy bottom, the water layer may be squeezed out from beneath the hull, robbing the sub of much of its upward buoyant force. In effect, the downward forces can then "glue" the sub to the bottom.