Geology Reference
In-Depth Information
Newberry Crater, at the western edge of the
suggested that Newberry Crater may again erupt, its
province, is situated at the apex of three converging
blanket of rhyolitic rocks tends to diminish that
fault zones, the easterly Brothers fault zone, the north-
possibility, because silica-rich rhyolitic lavas ordinarily
erly Green Ridge and Sisters fault zones, and the
appear very late in the life cycle of a volcano.
southwesterly Walker Rim fault zone. Placed at the
Lavas of the High Plains are distinctly bimodal.
center of these fracture patterns, it is little wonder that
That is, they have strikingly different compositions
Newberry volcano formed as a separate, younger
varying from dark-colored basalt to light-colored
eruptive site well to the east of the High Cascade
rhyolite. Basaltic lavas tend to have a deeper source in
vents. Today a small magma chamber may be less than
the crust and are extremely hot, while the lower
two miles below the caldera. Although it is often
temperature rhyolitic lavas are from chambers at
shallow depths. In addition, basalts are generally an
early stage of eruption, while rhyolites appear late in
Convergence of major structural features at New-
berry Volcano and volcanic features in the northwest
High Lava Plains.
