Most geology students know what a basalt or gabbro is, but occasionally even introductory texts will refer to different mafic rocks and ultramafic rocks. This list very briefly describes a few of these, just enough to differentiate between them based on composition and formation.
Mafic & ultramafic rocks
Types of volcanic eruptions and their dynamics
This post will focus on the processes driving volcanic eruptions (for more details on all things volcano, visit this awesome site by SDSU). The most important factor controlling eruption type is the composition of the lava, which controls how much gas the lava contains. The more viscous the lava, the more gas it traps—and the more gas, the more explosive the eruption.
Types of volcanic rocks, lava, and deposits
Volcanic rocks are extrusive igneous rocks. There are two main groups: rocks that form from the solidification of lava flows (extrusive), and rocks that form from the compaction of solid volcanic fragments (pyroclastic). This post will cover the basics in easy-to-grasp bullet-point style that facilitates comparison between volcanic rocks. For information on eruption types, click here.
Yellowstone volcanism: the three big eruptions
The Yellowstone Supervolcano, fed by a continental hotspot, has erupted many times over its 70 million year history, but three eruptions blanked the continent. Today, the sponge-like upper magma chamber is 80 km by 20 km, or 4,000 km3 by volume, of which 8% is molten; another deeper and larger magma reservoir, 46,000 km3 by volume, of which 2% is molten, lays 65 km beneath the ground. Despite its deceptive beauty, Yellowstone is an active volcano (perhaps most obviously evidenced by its frequent earthquakes) that will violently erupt at some point in the future. Read more →