Cliff and roadcut in ash-flow tuff along the Gardner river near Osprey falls, above
Mammoth. This is the Huckleberry Ridge tuff, which
erupted from the Island Park Caldera (SW of Yellowstone) about 2.1 million years ago.
The Huckleberry Ridge tuff here was several separate ash-flows, one on another while they were
still very hot, with some layers of falling ash in between. These layers cooled together and
welded into a thick dense rock. The different individual ash-flows now appear as the cliffs,
and the ash-fall as the thin layers forming slopes between the cliffs. Much of the Huckleberry
Ridge tuff has been eroded away since it erupted, but its original volume is estimated at
~3,000 cubic kilometers!
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Reconstructed distribution of ash-flow tuffs at Yellowstone after eruption of the Lava Creek
ash-flow tuff, 640,000 years ago (modified from Fig. 20 of
Christiansen, 2001). Remnants of the
the Huckleberry Ridge tuff (2.0 million years old) are in pink —. The Lava Creek
ash-flow tuff, in yellow, erupted with the collapse of the Yellowstone caldera. All
ash-flow tuffs at Yellowstone look very much like the Huckleberrry Ridge, and can be difficult to
sort out. The Lava Creek tuff has a total volume of ~ 1,000 cubic kilometers (a cube
10 km on a side), and thicknesses up to hundreds of meters (filling
pre-existing canyons). There have been no eruptions like this in recorded history.
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Broken piece of ash-flow tuff, from the roadcut. Tony Irving's finger points at the white spots,
which were pieces of pumice in the ash. The pumice was flattened (along with the ash shards) by
the weight of the hot ash over them.
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Geologists in their element - a roadcut on a busy highway. Tony Irving explains
how little bits of volcanic ash get compacted and cemented into massive rock, with
the proof of it as a backdrop.
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