Rhyolite Caldera Complexes
Rhyolite caldera complexes are the most explosive of Earth's volcanoes
but often don't even look like volcanoes. They are usually so
explosive when they erupt that they end up collapsing in on themselves
rather than building any tall structure (George Walker has termed
such structures "inverse volcanoes"). The collapsed
depressions are large calderas, and they indicate that the magma
chambers associated with the eruptions are huge. In fact, layers
of ash (either ash falls or ash flows) often extend over thousands
of square kilometers in all directions from these calderas. Fortunately
we haven't had to live through one of these since 83 AD when Taupo
erupted. Many rhyolite caldera complexes, however, are the scenes
of small-scale eruptions during the long reposes between big explosive
events. The vents for these smaller eruptions sometimes follow
the ring faults of the main caldera but most often they don't.
The origin of these rhyolite complexes is still not well-understood.
Many folks think that Yellowstone, for example, is associated
with a hotspot. However, a hotspot origin for most other rhyolite
calderas doesn't work; they occur in subduction-related arcs.
Examples of rhyolite caldera complexes include Yellowstone, La
Primavera, Rabaul, Taupo, Toba, and others.
This is an outcrop in the Los Chocoyos ignimbrite, the product
of one of the most powerful eruptions known...
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