Quicksand

The movement combined with an increase in pore pressure (of groundwater) leads to the loss of particle cohesion, causing buildings or other objects on that surface to sink.

To move within the quicksand, a person or object must apply sufficient pressure on the compacted sand to re-introduce enough water to liquefy it.

Since this increasingly impairs movement, it can lead to a situation where other factors such as exposure (i.e., sun stroke, dehydration and hypothermia), drowning in a rising tide or attacks by predatory or otherwise aggressive animals may harm a trapped person.

[3] Quicksand is a trope of adventure fiction, particularly in film, where it is typically and unrealistically depicted with a suction effect that causes anyone or anything that walks into it to sink until fully submerged and risk drowning.

[5] According to a 2010 article by Slate, this gimmick had its heyday in the 1960s, when almost 3% of all films showed characters sinking in clay, mud, or sand.