CRATER LAKE NATIONAL PARK
(photos from the textbook)
Crater Lake Caldera and Wizard Island. The caldera formed ~7700 years ago during an enormous, explosive, ash and pumice eruption of Mt. Mazama, a subduction zone stratovolcano in the Oregon portion of the Cascade Range. Wizard Island is a cinder cone.
CRATER LAKE NATIONAL PARK
(photos from the NPS)
The Pinnacles - Wineglass Welded Tuff, ~7700 years old. The light-colored
material at the bottom is dacite pumice and ash, erupted during the early
phases of the Mt. Mazama caldera-forming event. The gray-colored material
at top is andesite scoria and ash, erupted during the later phases of the Mt.
Mazama caldera-forming event. Molten dacite was originally in the upper
portions of the magma chamber, with molten andesite in the lower portions of
the magma chamber.
The tower structures, or "Pinnacles", are
the result of preferential lithification by fumarolic (steam vent) activity
when the deposit was fresh. Differential erosion has removed the loosely
consolidated ash-and-pumice/scoria materials.
CRATER LAKE NATIONAL PARK
(other photos)
Crater Lake Caldera and Wizard Island cinder cone.
Crater Lake Caldera and Wizard Island cinder cone.
Glacial striations on andesite at rim of Crater Lake Caldera.
Llao Rock at rim of Crater Lake Caldera. Medium gray = rhyodacite
lava. Light gray at top = rhyodacite ash & pumice from Mt. Mazama
caldera-forming eruption ~7700 years ago.