The Formation of Volcanic Centers
Volcanic centers within the southernmost Cascade Range are regions of large, long-lived, volcanic activity that erupt the full range of magma types (from low- silica basalt to high-silica rhyolite). They form when large bodies of basalt magma, which is very close to the composition of the mantle, rise through and collect in the crust. These low silica magmas are very hot and melt the crust; eventually the additional heat leads to the development of silica-rich magma bodies and eruption of silicic lavas (e.g. rhyolite). Volcanism in volcanic centers has been nearly continuous somewhere in the Lassen area over the past 3.5 m.y. Typically, a single volcanic center is active and becomes extinct before or as the next center begins. At Lassen, however, during the late Pliocene to early Pleistocene, the life spans of the Maidu and Dittmar Volcanic Centers coincided.