English: Mudcracks are diagnostic sedimentary structures indicating subaerial exposure of sediment surfaces, with alternating wet & dry conditions. They are much more common that raindrop imprints, which indicate the same environmental setting. Mudcracks are most likely to occur in fine-grained siliciclastic rocks, fine-grained carbonate sediments, and in some evaporitic successions. The examples shown above are in a volcanic hydrothermal area, specifically a dried-out hot spring.

Mudcracks are distinctive and easy to identify, but they do vary in appearance. The cracks themselves vary in width, depth, and areal density. Mudcrack polygons also vary in size & shape.

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From park signage: [This area has a] residual mass of cooling andesite lava perhaps 3 miles deep. The "rotten egg" smell is hydrogen sulfide fumes rising from deep within this mass.

Andesite lavas decompose readily but sulfuric acid and hot steam have greatly speeded up the process to carve out this barren, 16-acre bowl.

Bumpass Hell occupies the old eroded vent of a dormant dome volcano - Bumpass Mountain. More than 75 fumaroles, hot springs, and mudpots compose this 16-acre hydrothermal area.

The temperatures of each of the pools may vary. Which is all relative, of course, when "slightly cooler" means 150º Fahrenheit (66º Celsius), instead of 200º Fahrenheit (93º Celsius)!