7 - Volcano-Tectonic Earthquakes at Dacitic Volcanoes: Case Studies

Abstract

Eruptions of dacitic volcanoes may occur from the summit crater and the new vents on the flank of a volcano. The high-viscosity and relatively low-temperature magmas with great amount of volatiles are characterized by low mobility and high explosivity. The magmas may construct a lava plug dome, a cryptodome, or a lava spine in the crater of the volcano. Large volume of volatiles can produce numerous explosions of different intensity. Volcano-tectonic earthquakes can be observed during the movement of magma to the surface before lava extrusion. Lava effusion from summit and flank vents may be accompanied by volcanic tremor. Dacitic volcanoes have low altitude and stratovolcano shape. Summit eruption of dacitic volcanoes may consist of the growth of a dome in the crater with formation of lava flows and (or) a great explosion or a sequence of numerous small explosions. The most famous recent summit eruptions at dacitic volcanoes occurred at Mount St. Helens in the United States, Usu in Japan, and Pinatubo in the Philippines. Volcano-tectonic earthquakes are related to lava dome eruptions and magmatic explosions.