After lurking about on this blog since the beginning, and seeing so many requests for explanations of volcanic terms, I decided to try my hand at creating some vocabulary lists. So here’s one on types of volcanic eruptions. Unfortunately, different names have been applied to different eruption types over time, creating a fair amount of confusion. I have tried to indicate these where applicable.
There are several basic types of volcanic eruptions, which can be broken down by a combination of vent types and volume of ejected matter. A volcano, through its lifespan, will experience one or more of these types.
Effusive eruptions – eruption column <2 km. This really covers a range of types, all with the same basic characteristic of gentle flows of lava with low amounts of gas, thus producing low amounts of tephra or ash. The main types are Fissure, Flood, and Hawaiian eruptions.
Fissure Eruptions: These eruptions come through a fissure line or set of cracks in the ground instead of coming out of a volcanic crater. The Laki eruption is a prime example of this. The lava involved tends to form fire fountains, and be more liquid, allowing it to flow readily. Fissure eruptions can lead to the creation of a volcanic cone, as happened with Mauna Ulu, Hawaii.
Flood/Plateau eruptions: These are fissure eruptions, but on a much bigger scale. The volume is bigger and there are repeated large eruptions. The Deccan Traps (India) and the Columbia River Flood Basalt along the Snake River (USA) are a good examples.
Hawaiian eruptions: These are gentle eruptions that tend to come from a lava lake or central point instead of a fissure. Lava fountains several hundred feet high are normal.
Flank eruptions – these are eruptions coming through the flanks or sides of a volcano. They tend to occur when there is a combination of weaknesses in the rock forming the cone and not enough pressure behind the lava to get it to the top of the volcano. Some consider the ongoing eruption at Kilauea Volcano to be a flank eruption as it is occurring on the east flank of the volcano. Some have also called these fissure eruptions.
Submarine eruptions – these are eruptions that occur underwater. When they near the surface, they are indicated by discolored and boiling water, steam, and/or pumice rafts. The depth of the water at which to eruption occurs will affect the type of lava flow. This is an area of active research, and I have not found any definitive descriptions so far, though I think in the end that there will be multiple types defined.
Subglacial eruptions – these are eruptions that occur under glaciers. They are often indicated by sudden rapid increases in melt water (jökulhlaup) that are not seasonal. Icelanders know these very well. Due to the weight of the glaciers, it takes a substantial eruption to break the ice, and so a bit of steam and the abrupt release of melt water may be all that is visible of the eruption.
Summit eruptions – these are eruptions coming from a volcanic summit. This is the type of eruption most people will immediately think of when asked. The following are all summit eruption types:
Strombolian: eruption column <10 km. These are characterized by repeated small eruptions of cinder (most common), lapilli, and bombs to heights of a few tens or hundreds of feet. Sustained columns of ash are not created. Lava flows may or may not accompany the eruption. The name derives from the most common type of eruption at Stromboli in Italy. Magma tends to be basaltic and of a higher viscosity than that from Hawaii.
Peleean: These are violent eruptions of rhyolitic or andesitic lavas that tend to form lava domes, which then collapse and form pyroclastic flows. The name is derived from Mont Pelee in the West Indies. Some group these in with Plinian.
Plinian/Vesuvian: eruption column <45 km. These are powerful eruptions of gaseous siliceous lava (dacitic to rhyolitic) that can last anywhere from a few hours to weeks or months, and are the normal type of eruption for stratovolcanos. If enough lava is extruded, the cone can collapse and form a caldera. They produce large volumes of pumice and ash, and have a nasty habit of creating pyroclastic flows (such as the AD79 eruption of Vesuvius that took out Pompeii) and lahars. The name is derived from Pliny the Younger, who first described them via his report of the eruption of Vesuvius.
Sub-Plinian: eruption column <30 km. Same as Plinian, just smaller.
UltraPlinian: eruption column <55 km. Same as Plinian, just larger.
PhreatoPlinian/Phreatomagmatic: eruption column <40 km. This is the eruption of solid rock and steam. No new magma is released, it is all derived from surface or underground water hitting hot magma. These tend to form maars and tuff rings.
Surtseyan: eruption column <20 km. This is a stromblian eruption that involves a lot of water. The moist obvious example is the eruption and creation of the island of Surtsey off Iceland.
Vulcanian: eruption column <10 km. Gaseous silica magmas (andesitic to dacitic) are usually associated with these. They start with eruptions that clear the vent of old, solidified lava, progress through multiple explosions of ash and tephra, which produce large ash clouds, and will usually finish with a thick, viscous lava flow that tends to form domes. The SakuraJima eruptions are usually of this type. The name is derived from Volcano in Italy.
Primary sources of information:
http://volcano.oregonstate.edu/education/vwlessons/kinds/kinds.html. The primary sources for the classifications are MacDonald (1972), McClelland and others (1989), and Williams and McBirney (1979).