Travel Reference
In-Depth Information
[GEO.15]
. Streams of meltwater from the glaciers also carried away much of the debris and
then deposited it farther downstream as outwash sediments.
This kettle pond was formed when a melting glacier left a large piece of ice along with mixed sand,
gravel, and boulders. When that ice also melted, it left the hole that is now filled with water
[GEO.15].
The hot rocks underlying parts of Yellowstone had some unusual interactions with the
glaciers. The glaciers dammed many streams by simply filling the stream valley with ice. So-
metimes the lake that was formed behind the ice covered one of the many hot areas. Since
water boils at a higher temperature when under pressure, the increased pressure from the
lake caused the hot rocks below to
superheat
the surrounding groundwater. When the glaciers
melted, the ice dam sometimes collapsed suddenly, letting the lake drain rapidly. The super-
heated hot water at depth, suddenly relieved of the high pressure, boiled in a flash and created
a steam explosion that blew out much of the rock around it. Examples of this type of
explosion
crater,
now filled with water, are Duck Lake near West Thumb Junction
[GEO.16]
and Indian
Pond near Fishing Bridge Junction
[GEO.17].
Carving the Canyon
The magnificent Grand Canyon of the Yellowstone, with its steeply sloping sides, colorful
rocks, and spectacular waterfalls, was carved after the latest caldera-forming explosion
639,000 years ago.
Before the caldera existed, the Yellowstone River had been eroding the Absa-roka volcanic
rocks north of the present canyon area. Then came the Yellowstone Caldera eruption. A lot of
Lava Creek tuff blanketed the area, the caldera fell in, and rhyolites flowed out, nearly filling
the caldera with lava. All the while the Yellowstone River continued to carve its steep-sided
V-shaped valley
through volcanic debris, the caldera rim, and the lava flows.
