Travel Reference
In-Depth Information
The higher section of boardwalk (the former Grand Loop Road) returns you to the parking
lot, past large hot pools called the Painted Pools or Mimulus Pools, after the Latin name for
monkeyflowers. The pools show a range of colors. Some are clear, others opaque; some quiet,
others bubbling. To see several other geysers and hot springs, follow the lower boardwalk to
the left. This part of the geyser basin is especially prone to energy surges, that is, brief periods
when hot springs become geysers and known geysers increase their frequency and size.
It's hard to believe that the now relatively calm springs called Twin Geysers could ever
have been the largest geysers at West Thumb and a spectacular attraction, but in some decades
of the twentiethth century, this was the case. Rising temperature and boiling activity in 1998
preceded renewed eruptions that August and occasional eruptions since. The temperature in
one of the pools has sometimes measured 203°F (95°C)— above the boiling point of water at
this elevation.
Some of West Thumb's Painted Pools
The next notable feature is Blue Funnel Pool, an almost perfectly circular pool whose
shape somewhat resembles Morning Glory Pool.
Ephydra Spring was named in the 1960s for the brine fly (Ephydra bruesi) that is common
in alkaline thermal areas and feeds on microbes growing in the hot water.
Several springs lie in an almost straight line; apparently they have developed along a
slightly curving fracture under the earth. These springs include Blue Funnel, Ephydra, Per-
forated Pool, an unnamed pool with a black lining, Percolating Spring, Ledge Spring, and
Surging Spring. Some have erupted as geysers, including Ledge Spring during the summer of
1999 and into this century. On the opposite side of the walkway is humb Geyser— which
has been known to erupt up to 25 feet (7.5 m)—and also Collapsing Pool.
Continuing on the Grand Loop Road
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