What causes a volcano to erupt and how do scientists predict eruptions?
Attila Kilinc, head of the geology department at the University of Cincinnati, offers this answer. Most recently, Professor Kilinc has been studying volcanoes in Hawaii and Montserrat. When a part of the earth’s upper mantle or lower crust melts, magma forms. A volcano is essentially an opening or a vent through which this magma and the dissolved gases it contains are discharged. Although there are several factors triggering a volcanic eruption, three predominate: the buoyancy of the magma, the pressure from the exsolved gases in the magma and the injection of a new batch of magma into an already filled magma chamber. What follows is a brief description of these processes. As rock inside the earth melts, its mass remains the same while its volume increases–producing a melt that is less dense than the surrounding rock. This lighter magma then rises toward the surface by virtue of its buoyancy.
Volcanoes are the result of the dynamic of Earth. Earth’s crust is broken in many blocks (tectonic plates) that are in motion respect one another. Mostly of volcanoes are located along boundaries of adjacent plates. Volcanic eruptions near tectonic plates’ boundaries are driven by the magma that ascend from deeply beneath the crust Scientific predict volcanic eruptions by studying some geophysical and geochemical parameters: * increasing of the seismic activity near the volcano * changes in the quantity of gases (CO2, SO2, etc) expelled by the volcano * observed changes in magnetic or geoelectrical explorations: studying the surface of the volcano with magnetic geoelectrical methods.
Volcanoes are “born” when magma (liquid rock inside the earth) reaches the surface. Depending on the type and duration of the eruption lava and or tephra can pile up to make a volcano. You might enjoy reading “Birth of Volcanoes” by Maurice Krafft (in Volcanoes Fire from the Earth: Abrams Discoveries, 208 p.). Volcanoes erupt because of buoyancy and gas pressure. Buoyancy is a force that causes lighter material to rise through surrounding denser material (think of a hot air balloon rising in the cooler air). The hot liquid magma rises towards the surface through the more dense rock. Gas pressure from gas dissolved in the magma also exerts force on the surrounding rock. It cracks the rocks above the magma and then moves into the crack. This process repeats many times until the magma reaches the surface.
When a part of the earth’s upper mantle or lower crust melts, magma forms. A volcano is essentially an opening or a vent through which this magma and the dissolved gases it contains are discharged. Although there are several factors triggering a volcanic eruption, three predominate: the buoyancy of the magma, the pressure from the exsolved gases in the magma and the injection of a new batch of magma into an already filled magma chamber. What follows is a brief description of these processes.
monitoring of volcanoes can be done using numerous methods which allow volcanologists to predict eruptions: mapping of ancient deposits – mapping of previous deposits allows an understanding of future eruptions i.e. ignimbrite and pumice deposits will hint at future plinian style eruptions, whearas lava flows will hint at effusive strombolian or hawaiian eruptions. placing seismometers both onto and around a volcano allows the monitoring of small earthquakes and the tracing of magma as it moves towards the surface. it is important to place seismometers further away from the volcano to monitor regional activity, so as not to confuse and complicate the data collected. tiltmeters – allow the monitoring of ground deformation, bulging caused by intrusion of magma beneath the ground. this may be indicative of an iminent eruption. also, monitoring of small eruptions may show juvenile and or accidental material. accidentals (country rock) may show the eruptions to be phreatic only, when heated