Geological Survey Fact Sheet —, 4 p. This explosion was the most powerful in a series of eruptions during —17 that were the last to occur in the In modern times, volcanic phenomena have attracted intense scientific interest, because they provide the key to understanding processes that have created and shaped more than During the past 4, years eruptions have occurred at an average rate of about 2 per century.
How Does a Volcano Erupt? While many people envision a conical peak when they think How do volcanoes arrupt a volcano, a wide variety of landforms fall into the category, including midocean ridges and the fissures that erupt great sheets of flood basalts.
Volcanic eruptions may be rather quiet and slow-paced, or they may be dramatically violent and catastrophic. Sources of Volcanoes Volcanoes are typically found in two major sites on the planet: Divergent plate boundaries are rifts where upwelling lava forms fresh oceanic crust at submarine volcanoes.
Eruption Basics The eruptive behavior of a given volcano largely depends on the gas and mineral content of the magma that feeds it.
Gases, called volatiles, include water vapor as well as carbon dioxide, sulfur dioxide and other elements. These volatiles are pressurized at depth and expand as the magma nears or attains the surface.
A silica-rich magma is more viscous -- that is, it flows less easily -- and impedes gas release more significantly than a low-silica, more fluid magma. Thus magmas heavy in silica are more prone to explosive eruptions as pent-up gases build up intense pressure.
The relative amount of silica in lava helps classify it: Basaltic lava is low in silica; andesitic lava, intermediate; and dacitic and rhyolitic lavas are rich in silica. These categories can explain eruptive behavior and also describe the rock types ultimately formed from hardened lava -- geological formations hinting at past volcanic activity.
Sciencing Video Vault Eruption Phenomena A volcanic eruption may emit lava flows, gases and pyroclastics, which are the debris of lava or crustal rock shattered in the explosion.
Pyroclastic material, also called tephra, ranges from huge blocks and bombs to pulverized cinders and ash. Along their margins, they may kick up billows of gas-flared ash -- pyroclastic surges -- which, unlike the flows, can clear topographical barriers and travel impressive distances.
Also formidable are lahars, water-saturated flows of debris -- unleashed, for example, by rapidly melting summit glaciers -- that can race down river valleys draining volcanoes.
Types of Explosive Eruptions A common categorization scheme for explosive eruptions names each type after specific volcanoes that exemplify it. Hawaiian eruptions are usually quiet flows of basaltic lava. Strombolian eruptions describe nearly continuous eruptions of gaseous lava at intermediate intensity, often characterized by small blasts tossing lava clods into the air.
Vulcanian eruptions are more explosive yet: Gases accumulate beneath crust built by viscous lava, ultimately bursting forth to spew pumice and a great cloud of ash. Those scorching avalanches also characterize Plinian eruptions, exceptionally powerful events that produce titanic ash clouds and sometimes the collapsed craters called calderas.Volcanic eruptions can either be effusive or explosive.
An effusive volcanic eruption occurs when the lava pours out onto the ground from the volcano's vent. When the molten rock or magma is thin and runny, gases can easily escape and the lava flows freely and travels far.
When the lava flows easily, it can travel far and create wide shield volcanoes. When the lava is very thick, it creates a more familiar cone volcano shape (aka. a cinder cone volcano).
When the lava is very thick, it creates a more familiar cone volcano shape (aka. a cinder cone volcano). When the lava is extremely thick, it can build up in the volcano and explode (lava domes). Nov 22, · A volcano erupts when pressure on the magma chamber causes the magma to rise and come out together with gas, rocks and ashes.
The violence of an eruption depends on how much pressure the volcano. Volcanoes are typically found in two major sites on the planet: at the boundaries of tectonic plates and at so-called “hotspots,” where magma rises from much more discrete heat sources in the mantle.
Volcanoes are rare locations on the Earth’s crust where molten rock (magma) spews to the surface as lava, often accompanied by superheated gas and debris.