Classification of Volcano: Eruption Style Pt 2 (Final)

Peléean eruptions

Pyroclastic flow resulted from the eruption of Mt. Pelée at 1902.
Source: http://volcano.und.edu/vwdocs/volc_images/north_america/XXVI.jpg

These eruptions involve viscous magma and shares characteristics with Vulcanian eruptions. They are usually violent and destructive and hence usually resulting in much of the volcano being blown apart. They occur when the gas is highly sticky magma builds up tremendous pressure. This pressure results in a large quantity of gas, dust, ash, and incandescent lava fragments being blown out of a central crater, fall back, and form tongue-like, glowing avalanches that move downslope ("nuées ardentes") at velocities as great as 100 miles per hour. Some of these eruptions may produce domes or short flows or ash and pumice cones. This type of eruption was first described at Mt. Pelée.

Vulcanian Eruptions

An ash-rich vulcanian eruption plumerises above Sabancaya volcano in northern Perú on April 15, 1991.
Source: http://www.volcano.si.edu/world/tpgallery.cfm?category=Pyroclastic%20Fall&photo=047076

Vulcanian eruptions are characterised by the eruption of solid rock and steam. They initially occur as a series of discrete, canon-like explosions that are short-lived, lasting for only minutes to a few hours, often with high-velocity ejections of bombs and blocks. After which, the subsequent eruptions can be relatively quiet and sustained. The fragments deposited by the eruptions can be from ash to blocks in size and cold to incandescent in temperature.

These eruptions are more explosive as compared to Strombolian eruptions as the eruptive columns are normally within 5-10 km high. The amount of tephra produced is relatively small, but due to the explosive nature of the eruption, it is dispersed over a wide area.

Vulcanian eruptions are often connected to andesitic to dacitic magma. The viscous magma makes it difficult for the gases to escape, this leads to the build up of high gas pressure and results in explosive eruptions.

Plinian Eruptions

Klyuchevskaya eruption, Kamchatka in 1994
Source: http://www.geology.sdsu.edu/how_volcanoes_work/Images/Eruptions/Klyuchevskaya_crop_l.jpg

Plinian eruptions are explosive and are associated with volatile-rich dacitic to rhyolitic lava, which erupts from stratovolcanoes. The eruptions are highly variable, lasting from several hours to about 4 days. Although Plinian eruptions characteristically involve felsic magma, they can occasionally occur in fundamentally basaltic volcanoes where the magma chambers become differentiated and zoned to create a siliceous top.

Rather than producing the discrete explosions that are typical of Vulcanian and Strombolian eruptions, Plinian eruptions generate sustained eruptive columns. Although they differ markedly from non-explosive Hawaiian eruptions, Plinian eruptions are similar to Hawaiian fire fountaining in that both of these eruption types generate sustained eruption plumes. In both, the eruption plumes are maintained because the growing bubbles rise at about the same rate as the magma moves up through the central vent system.

Plinian eruptions generate large eruptive columns that are powered upward partly by the thrust of expanding gases, and by convective forces with exit velocities of several hundred meters per second. Some reach heights of ~45 km. These eruptive columns produce widespread dispersals of tephra which cover large areas with an even thickness of pumice and ash. The region of pyroclastic fall accumulation is generally asymmetric around the volcano as the eruptive column is carried in the direction of the prevailing wind.

Most of the composite volcanoes tend to erupt in this manner. Fast-moving deadly pyroclastic flows, also known as nuées ardentes, are also commonly associated with Plinian eruptions.