Soil

Is soil a solid or a liquid? Both, if we abuse the English "or" in the inclusive sense, rather than the exclusive that some might expect. Soil is solid, except when it is not, probably when there is too much water or maybe too much vibration. Humans like to noun things, which can pigeonhole when there is a continuum from soil with some water in it to water with some soil in it, and some interesting states between, depending on the exact conditions. Soil itself is a vague term; one might find phase diagrams with varying amounts of sand, clay and I forget what the third part was, the geology classes having been a while ago now. Anyways, those interesting states. Too much water and soil can suddenly liquefy, which is called liquefaction, perhaps problematic during an earthquake, or when one is too close to quicksand for comfort. Soil usually holds itself together by friction. Enough water can "unlatch" that friction and now you've got more a liquid with solid bits than a wet solid. Another cause of liquefaction is when there is too much water pressure, which may force the soil grains apart. Water pressure is a feature of dams, and probably should be managed correctly by those dam engineers.

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