Travel Reference
In-Depth Information
In 1991,
Black Pool
became much hotter than before and erupted for a brief period. This
activity killed the bacterial mats, whose oranges and browns had combined with the usual
blue of the water to give the pool an almost black color. Now Black Pool is often a lovely blue
or green and is gradually cooling.
West Thumb is anything but a static place! Proof of this is given by the recent history of
Abyss Pool.
A very explosive geyser in the early years of the twentieth century, Abyss then
became dormant for something like 80 years. Then in 1991 and 1992, it erupted numerous
times up to 100 feet (30 m), causing some of the nearby pools to drain. Since then, Abyss has
quieted, but no one can guess how long it may remain that way. At 53 feet (16 m) deep, it's
one of the park's deepest pools. It's sometimes difficult to see the bottom through the lightly
bubbling blue-green water.
As you ascend the boardwalk's hilly stretch, you can see that trees to your left have been
killed by mineral-laden water. In this area,
Hillside Geyser
was erupting to 70 feet (20 m) or
more between 1995 and 2005.
Black Pool turned blue in 1991.
To the west of the boardwalk intersection beyond the Twin Geysers overlook, an unnamed
steam vent often makes a furious racket. Just above here, road builders many years ago diver-
ted the steam of a fumarole away from the construction site by cramming a pipe into it. The
pipe ends here.
