Travel Reference
In-Depth Information
West Thumb Geyser Basin
Walking toward the lake from the parking lot, stay to the right to find the
Thumb Paint Pots
[GEO.23],
named Mud Puffs when the pastel colors were remarkable in the nineteenth cen-
tury. Now they are duller and vary from muddy to dry depending on recent rainfall. The mud
is formed by sulfuric acid in the water acting on the rock as it passes through.
Seismograph
and
Bluebell Pools,
on a spur to the right, differ from each other in temper-
ature and sometimes in coloring. Seismograph's name dates to about 1960, when it was no-
ticed that small earthquakes caused turbidity and a rise in the pool's temperature. There may
be extremely thick, colorful mats of bacteria and algae in both pools' runoff (see “What Makes
the Colors?” on
page 65
).
At the lakeshore are
Lakeside Spring
and
Venting Pool,
unremarkable features when
they're cool. However, when Lakeside Spring's water is hot, its microorganisms are beautifully
colored. Look down from the boardwalk to see a remnant of the concrete that supported a
boat dock here a century ago. A sign explains the West Thumb caldera.
