5 - Volcano-Tectonic Earthquakes at Basaltic Volcanoes: Case Studies

Abstract

Basaltic volcanoes have characteristic lava of low viscosity (10–103 P), high temperature (1000–1300° C), with a small amount of volatiles (0.22 wt.%), and high velocity of movement. They are characterized by Hawaiian and Strombolian types of eruption and produce extensive lava flows. The eruptions of basaltic volcanoes may occur from the summit crater of the volcano, but flank or fissure eruptions are very frequent too. The low-viscosity and high-temperature magmas are very mobile and able to form the passageway to the surface along or out of the central conduit of a volcano. These properties of magma constrain the possible seismic reaction to the magma movement. The fracturing of rock during the forming of new volcanic vents on the flanks of a volcano or along a new fissure produces volcano-tectonic earthquakes. These earthquakes can be observed also during the movement of magma along the volcanic conduit before the summit eruptions. A stratovolcano is a volcano constructed of alternating layers of lava flows and pyroclastic rocks. Stratovolcanoes are steeper than shield volcanoes and tend to a conical form. A fissure eruption is an eruption that takes place from an elongate fissure, rather than from a summit vent. A caldera is a gigantic basin with steep walls at the summit of a volcano; larger than a crater. It is usually formed by collapse. The multiple stages of collapse following evacuation of underlying magma chamber are characteristic for Kilauea (Hawaii) and Fernandina. Submarine eruptions vary between its birth on the deep seafloor and its emergence above sea level.