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Yellowstone's Hydrothermal Features

Remnants of an ancient volcano - boiling hot springs, geysers, mud pots, and
steam vents - are evidence of Yellowstone's violent geologic history. The world's
highest concentration of hydro (water) thermal (heat) features is found here.

Norris Geyser Basin (30 mi. North)

Fumaroles or steam vents are hot springs
without enough water to erupt or flow. The
small amount of available water quickly boils
away, leaving only steam and gases to escape.
Steam vents usually occur on higher ground.

Grand Prismatic Spring,
Midway Geyser Basin (6 mi. Nort)

Hot springs are pools of heated water with
temperatures ranging from tepid to boiling.
Their plumbing system varies from narrow
to wide. Water circulation is continuous;
cooler surface water sinks while hotter
water rises.

Castle Geyser,
Upper Geyser Basin

Cone geysers function similarly to a nozzle
spouting water. Deep within the earth, heated
water dissolves and then transports silica, the
same mineral found in sand and glass, to the
surface. During geyser eruptions, silica is
deposited around narrow "vents" or openings.
Over time this mineral, called geyserite or sinter,
forms mounds of varying sizes and shapes.

Grand Geyser,
Upper Geyser Basin

Fountain geysers have larger surface openings
that fill with water before or during an eruption.
When not erupting they can be mistaken for hot
springs. To tell the difference, look carefully at
the feature. Hot spring water levels remain
relatively constant while those in fountain
geysers fluctuate. Geyser runoff channels contain
little or no water and are often dry and whitish
grey. Active hot spring channels are wet and
generally quite colorful.

Bubbling Mud,
Fountain Paint Pots (8 mi. North)

Mud pots are pools of scalding mud lying over
steam vents. Mud pots form when gases interact
with surface water and organic matter to create
acid. The acid breaks down mineral-laden rock
into clay creating a viscous and often colorful,
bubbly mix. Mud consistency depends on the
amount of water present.

Don't miss the rest of our virtual tour of Yellowstone National Park in 4870 images.