Quick Sand, YIKES!
The land that is soft and wet and yields to pressure is called marshland or a marsh. It is characterized by waterlogged soil and the growth of wetland plants. Marshes are found in coastal areas, river floodplains, and other low-lying areas with high water levels.
Quick sand, bog and muskeg all have such properties.
A marsh or swamp typically fits this description - both are low-lying wetlands characterized by soft, waterlogged soil that yields to pressure. These environments are typically rich in organic matter and support a variety of plant and animal species adapted to the wet conditions.
swamp
marsh
In the ocean the sand and seaweed at the bottom of the water are very wet and moist. Its like silk (very soft). So the land at the bottom of the ocean is wet and full of moisture.
Soft wet ground is called "mud."
Marsh
houses and buildings on wet land.......
A sponge can be both soft when wet and rough when dry.
because it gets wet and soft
soft and wet