The Cascade Volcanic Arc is a chain of volcanoes stretching from southern British Columbia down to northern California. Within the arc there is a variety of stratovolcanoes like Mount Rainier and broad shield volcanoes like Medicine Lake. But calderas are very rare in the Cascades, with very few forming over the 39 million year lifespan of the arc.
The few eruptions that do form calderas rarely make it into the VEI 7 range, staying confined to the VEI 6 range in most cases. The only volcanoes known to have produced eruptions within the VEI 7 range are Crater Lake, the Mt. Baker Volcanic Field, and the Lassen Volcanic Center.
All of the exceptionally large caldera-forming eruptions within the cascades erupted silica-rich magmas, with the three VEI 7s erupting mainly rhyodacite and rhyolite.
List of calderas +VolcanoCaldera NameCaldera SizeAgeEruption Unit NameMagma Volume (km3)Tephra Volume (km3)VEINotesReference(s)SilverthroneSilverthrone caldera20 km wide<1,100,000N/AN/AN/APoorly studiedFranklin Glacier ComplexN/A6 x 20 km<6,800,000N/AN/AN/APoorly studiedCoquihalla Volcanic ComplexN/A6 x 6 km<21,400,000N/AN/A50Tephra volume does not represent a single eruptionHannegan Hannegan caldera8 x 3.5 km3,722,000Ignimbrite of Hannegan PeakN/AN/A6-7Trap-door caldera, first collapse. Both ignimbrites have a combined magma volume of 127 km3 3,720,000Ignimbrite of Ruth MountainN/AN/A6-7Trap-door caldera, second collapseBig Bosom ButtesBig Bosom caldera4 x 5 km ?OligoceneN/AN/AN/APoorly studiedMount Rahm ?Mount Rahm calderaN/AOligoceneN/AN/AN/APoorly studiedMount Baker Volcanic FieldKulshan Caldera4.5 x 8 km1,149,000Lake Tapps tephra124N/A7Gamma Ridge ?Gamma Ridge calderaN/A1,242,000N/A40N/A6-7Poorly studied, trap-door calderaMount Aix Volcanic ComplexMount Aix caldera6 x 928,000,000Bumping River tuff-northN/AN/A6-7Cummalitave volume of Mt. Aix tuffs exceeds 100 km325,000,000Bumping River tuff-eastN/AN/A6-725,000,000Cash Prairie tuffsN/AN/A6-7Goat RocksDevils Horns caldera5 x 8 km3,200,000N/AN/A>606Tephra volume may represent multiple eruptionsNewberryNewberry Crater6.4 x 8 km80,000Olema ash14-22N/A6Second caldera formation230,000Tepee Draw tuff10256First caldera formationMount MazamaCrater Lake8 x 10 km5783 BCEMazama ash611767Largest Holocene eruption in the arc29,900Trego Hot Springs820.86Medicine LakeMedicine Lake caldera7 x 12 km171,000Antelope Well tuff20N/A6Lassen Volcanic CenterRockland calderaN/A610,000Rockland tephra130326.77
Places where calderas could be These are places that have experienced very large eruptions of ash and ignimbrite that reached a VEI of 6 or greater, but have no documented calderas.
Tumalo Volcanic Center The Tumalo Volcanic Center is a volcano located just east of Bend, Oregon. It started producing large eruptions around 650,000 years ago, with its first eruption reaching a 5 on the VEI scale and erupting more than 1 km3 of magma. The volcano would go on to produce at least three more voluminous eruptions. The two largest eruptions ejected more than 5 km3 of magma. Eruptions of those sizes usually entail caldera collapses. However no calderas have been identified in this area.
Deschutes Formation Between 6.25 and 5.45 million years ago the cascade volcanic arc flared up in activity. Producing far more explosive ignimbrite eruptions than usual. The activity was mostly focused within the central Oregon cascades. Over 78 individual eruptions have been identified and the total volume of pyroclastic products in the Deschutes formation is estimated to be between 400 and 675 km3.
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