Types of Explosive Volcanic Eruptions

Can volcanoes be classified by comparing volcanic deposits to observations of historic eruptions?

Volcanoes occur in various locations of the Earth and erupt in different styles- sometimes quietly oozing like lava flows in Hawaii or explosively erupting like Mt. Pinatubo in the Phillippines.

Traditionally, deposits from explosive volcanic eruptions have been classified by comparing to the deposits from well-recorded eruptions observed in historic time. Some examples are:

• Strombolian named for Volcan Stromboli in Italy in which discrete bursts of activity occur.
• Hawaiian named for the types of spattery lava that is observed in "fire fountains" in Hawaii.
• Plinian named after Pliny the Younger who recorded the A.D. 79 eruption of Mt Vesuvius, a cataclysmic event which blanketed the city of Pompeii and spread volcanic ash far and wide.
• Surtseyan named for a volcano which erupted off the coast of Iceland, in which sea water mixed with hot lava for explosive eruptions.

Many problems exist with this classification scheme. Some of the case study volcanoes can display different styles of eruptions over time. The other problem is that in the study of past volcanic history, there are no recorded observations and must deduce the style of eruption by studying the deposits left behind.

A scheme proposed by G.P.L. Walker in 1973 addressed this second problem by developing a criteria based upon field measurements of volcanic deposits. Volcanoes are classified by a measure of "dispersion," how far the deposits are found from the volcano versus a measure of "fragmentation" which corresponds with how explosive the eruptions were. These match well with observations of the height of eruption column and estimated degree of explosiveness.

While many geologists do not fully agree with a rigorous classification scheme, associating volcanic eruptions to the "case" examples has proven useful for understanding the larger picture of how the form and where volcanoes occur.

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Walker, G.P.L., 1973, "Explosive Volcanic Eruptions-- a new Classification Scheme," Geologiche Rundshau, vol 62, 431-446.