Figure 14.6

Three types of lava. (A) Mafic lava has a low viscosity and flows in streams or sheets downslope. This volcanologist (a scientist who studies volcanoes) is sampling pāhoehoe in Hawai’i Volcanoes National Park, on the island of Hawai’i. (B) Intermediate lava is more viscous than mafic lava and resists movement. This photo shows the blocky consistency of intermediate lava on Mount Etna, Sicily. (C) Thick, felsic lava has formed a plug dome in the volcanic vent of Mount St. Helens.

(Top, © David R. Frazier/Science Source; center, © Tom Pfeiffer/www.volcanodiscovery.com; bottom, USGS/photo by John S. Pallister)