Sand boil

[3] Adjacent sand blows aligned in a row along a linear fracture within fine-grained surface sediments are just as common, and can still be seen in the New Madrid area.

These earthquakes also caused the largest known sand boil in the world, which can still be found near Hayti, Missouri and is locally called "The Beach".

The presence or absence of soil liquefaction features, such as clastic dikes, is strong evidence of past earthquake activity, or lack thereof.

Sand boils are caused by hydraulic head in levee or dike pushing the water to seep out the other side, most likely during a flood.

[6] During the flood of spring 2011, the United States Army Corps of Engineers had to work to contain the largest active sand boil ever discovered.

By mapping the location of sand boils that erupted in the Marina District during the 1989 Loma Prieta earthquake, scientists discovered the site of a lagoon that existed in 1906.

Sand boils that erupted during the 2011 Canterbury earthquake .
Attempts to plug a sand boil with sandbags during the 2011 Missouri River floods . Many of the attempts were unsuccessful.
Sand boils and a silt-covered street after the 2011 Canterbury earthquake.
Cross section of a sand volcano in County Clare, Ireland