If gas bubbles in the lava were trapped as the rock cooled, they form vesicles in the basalt. Basalt is ubiquitous in eastern Washington. The order in which minerals crystallize from a magma. The composition of the remaining magma can be greatly altered by early crystallization, helping to give us the diversity of volcanic and plutonic rocks we see in igneous terrains. Breccia Volcanic rocks made of angular clasts which often form at the top of lava beds when the lava cracks as it flows.
Craters are small compared to calderas.
Craters can occur within calderas. Hot Spot A portion of the mantle that, for one reason or another, is abnormally hot. We think the Hawaiian island chain was formed by oceanic crust moving over a hot spot. Some geologists think the Cenozoic flood basalts in eastern Washington and southern Idaho, and Yellowstone s volcanism, all owe their origins to one hot spot over which the North American plate has been moving. Obsidian The glass produced if lava forms very quickly from water-poor magma and no crystals have time to form.