Active Volcano; Eruption Duration; Eruption Size

In the last few hundred years the largest volcanic eruption was of VEI:

7

Earthquakes:

A moderate magnitude local earthquake can cause sufficient ground shaking that a gravitationally unstable volcano flank can collapse, generating a debris avalanche. This occurred at Mt. St. Helens in 1980, Cordon Caulle volcano, and 7.2 Landers earthquake

Active volcano

A volcano which has erupted during recorded history: About 500 volcanoes worldwide are active by this definition. A volcano which has erupted in the last 10,000 years: More than 1,400 volcanoes worldwide are active by this definition.

Dormant volcano

A volcano which is not active but which will erupt again. Determined by the repose time. Most dangerous volcanoes. The number of dormant volcanoes worldwide is not well known

Erupting volcano

A volcano with an eruption taking place. Individual eruptions can typically last from days to tens of years (see below).

Rainfall

Can trigger the explosion and/or collapse of a lava dome, producing pyroclastic flows. Example at Montserrat in March, 2000

Small eruptions occur much more frequently than large eruptions.

For example, compare the frequency ("How Often") of VEI 1 eruptions with VEI 5 eruptions.

Compared to a volcanic eruption of VEI 3, an eruption of VEI 6 is ____ times larger.

One thousand

In recent times, 'large' eruptions haven't actually been all that big.

The 1980 Mt. St. Helens eruption was 'only' VEI 5, and the 1991 Pinatubo eruption VEI 6.

Debris avalanche

The removal, by avalanching, of a large rock mass from above the magma chamber will depressurize the magma, causing instantaneous vesiculation and explosive eruptionExample: A debris avalanche began the 1980 eruption of Mt. St. Helens.

At any given time

approximately 15 volcanoes are erupting on Earth and, on average, 70 volcanoes (ranging between 60 and 80) are in eruption every year

most eruptions

are small and/or remote from populated areas, and commonly not deemed 'newsworthy'.

eruption

ejection of lava and/or rock fragments from a volcano

Mass Magnitude

eruption magnitude which is fully quantitative and directly comparable to the Richter earthquake magnitude,

Magma chamber recharge

eruption trigger. Intrusion of 'fresh', typically basalt, magma into the bottom of a magma chamber

largest known basaltic eruptions

flood basalt eruptions, involving the outpouring of hundreds of thousands to millions of cubic kilometres of lava

In the past few hundred years there have been some very large eruptions.

he two largest eruptions in the past 200 years were from volcanoes in Indonesia, the 1883 Krakatoa (Krakatau) eruption [VEI 6] and the 1815 Tambora eruption [VEI 7].

Eruptions: How Long?

most volcanic eruptions last between 1 and 100 days. about 10% have lasted for no longer than one day. Stromboli (the "lighthouse of the Mediterranean") has been erupting nearly continuously for 2,500 years. Smaller volcanoes tend to have eruptions of shorter duration; for example, of observed scoria cone eruptions, 50% lasted less than 30 days, and 95% stopped within one year.

Mundus Subterraneus by Athanasius Kircher, published in 1665

one of the earliest, if not the first, world map to indicate the known volcanoes at the time of publication. There are 34 volcanoes (montes vulcanios) indicated on Kircher's map

La Garita eruption

one of the largest known explosive eruptions

Vesiculation

results in magma chamber pressurization and, ultimately, in overpressure in the magma chamber

Volcanic Explosivity Index (VEI)

size of an explosive volcanic eruption. VEI is based on the volume of tephra erupted.

VEI 8 - 'mega-eruptions' from 'supervolcanoes', all of rhyolite and caldera-forming. The most recent VEI 8 was the Taupo, New Zealand, eruption 26,500 years ago.

such eruptions have a profound global impact, resulting in long-term climate effects. The Toba eruption, 74,000 years ago (Indonesia), caused a prolonged 'volcanic winter' and the Yellowstone eruption, 2 million years ago, distributed air-fall ash over much of the area of the present-day U.S.

largest basaltic eruption in historic time

the 1783-4 Laki, Iceland, eruption,

repose time of a volcano

the average period of time between eruptions of the volcano

Eruptions: How Large?

the best way of measuring the size of an eruption is: The volume of tephra ejected in the eruption;

Gases in magma

the single most common trigger for eruptions

above sea-level (subaerial) volcanoes

there are about 1,400 active (defined below) volcanoes and a not-well-known number of dormant and extinct (also defined below) volcanoes

Hawaiian eruptions

typically are VEI 0 or 1 but the largest historic eruptions - 1950 Mauna Loa and the 1983-2018 Kilauea eruptions - have a mass magnitude in the 5.0 to 6.0 range,

fumaroles

where volcanoes constantly vent gas from