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A subduction zone is formed where two tectonic plates come together and one plate overrides the other. The plate with lower density, usually comprised of continental crust, stays on top while the denser plate, usually made of oceanic crust, is pushed and pulled beneath, into Earth’s mantle.

A spreading center is formed where two tectonic plates are moving away from each other. Magma from the mantle upwells to fill the space made by the diverging plates, and erupts at the boundary to form new crust.

The Salton Buttes volcanic field is the youngest and southernmost of the fields associated with the North American and Pacific plate boundary. Five obsidian rhyolite domes erupted on the southern shore of the Salton Sea between 6000 and 500 years ago. The area is active geothermally and seismically, with numerous hot springs and mudpots on the surface. 

Transform boundaries are formed where two tectonic plates pass laterally by one another. These boundaries are commonly defined by a series of faults, each of which accommodates some of the translational movement between passing plates. Small bends in these boundaries led to the formation of mountains and valleys.

The Mendocino Triple Junction is a tectonic boundary where three plates (the Pacific, North American, and Juan De Fuca) meet. 

USGS Hawaiian Volcano Observatory geologists collected a sample of the middle East Rift Zone Kīlauea eruption in Nāpau Crater, within a closed area Hawaiʻi Volcanoes National Park. Geologists put molten lava into a metal bucket and rapidly quench it with water.