Many of trail guides, books, and informational signs about the eruptions at Yellowstone talk of the volcanic ash that covered huge areas of the continent following the massive eruptions. The largest of these spread volcanic ash from California, to Louisiana, and up into Canada. As you might expect, near the source the layer of ash is thickest and thins out to the edges.
So what is this volcanic ash? It is a mixture of rock, volcanic glass pieces that are less than 2 mm and often less than 0.025 mm (1/1000th of an inch). While it resembles ash from fires, it does not act like it. Volcanic ash is extremely abrasive, slightly corrosive, and electrically conductive.
Volcanic ash is formed during violent, explosive eruptions. The eruption blows apart rock and sprays tiny pieces of magma into the air where it cools into microscopic pieces of volcanic glass creating the typical towering cloud above eruptions. When the ash falls to the ground, it could still be hot enough to fuse together into a solid rock called a tuff or welded tuff.
The cliffs here are composed of volcanic ash from one of Yellowstone’s eruptions.
Logging requirements:
Send me a note with :
- The text "GC15A1C Tuff Cliff" on the first line
- The number of people in your group.
- from the safety of the picnic area examine the cliffs and see if you think this ash was hot enough to weld together when it covered the landscape.
- compare your answer to what the sign says
- From the sign find out what is tearing apart the cliff.
The above information was compiled from the following sources:
- NPS informational Pannel
- http://volcanoes.usgs.gov/Products/Pglossary/ash.html
- http://pubs.usgs.gov/fs/2005/3024/ (ash map)
Placement approved by the
Yellowstone National Park