Ultramafic rock but there are ultrapotassic and highly silica-under-saturated rocks with >18% MgO which can be considered "ultramafic". Ultrapotassic, ultramafic igneous rocks such as lamprophyre, lamproite and kimberlite are known to have reached the surface of the Earth. Although no modern eruptions have been observed, analogues are preserved. Most of these rocks occur as dikes, diatremes, lopoliths or laccoliths, and very rarely, intrusions. Most kimberlite and lamproite occurrences occur as volcanic and subvolcanic diatremes and maars; lavas are virtually unknown. Vents of Proterozoic lamproite (Argyle diamond mine), and Cenozoic lamproite (Gaussberg, Antarctica) are known, as are vents of Devonian lamprophyre (Scotland). Kimberlite
Geology of the Lassen volcanic area called the Chaos Jumbles. The first and largest of these traveled downslope and was able to climb up the side of Table Mountain. The trigger for the rockfall is unknown, but it was most likely a large earthquake. Normal weathering also weakens fractured volcanic rock and contributes to small rockfalls. In the summer of 1994, a rockfall of occurred on the northeastern flank of Lassen Peak. During periods of extreme rainfall or snow melt, mudflows are sometimes generated by mobilization of loose volcanic debris and soil on the slopes of volcanoes. The only current visible activity in the Lassen volcanic