Examples: Tambora, Vesuvius, and Toba
The great Tambora eruption of 1815 and its aftermath
The bright sun was extinguish’d and the stars
Did wander darkling in the eternal space,
Rayless, and pathless, and the icy earth
Swung blind and blackening in the moonless air;
Morn came and went – and came, and brought no day…..
An extract from "Darkness” by Lord Byron, written in June 1816 on the shores of Lake Geneva in the midst of the Year Without a Summer, 14 months after the great eruption of Mount Tambora in Indonesia.
1816 is probably the best known example of a volcanically-induced climate cooling event. It was largely caused by the eruption of Tambora, Indonesia, in April 1815, in one of the largest known eruptions of the past few millennia. The aerosol veil caused Northern Hemisphere cooling of up to 1 degree Celsius, and considerably more locally, with effects lasting until the end of 1816 and extending to both hemispheres. Snow fell in New England in June and abnormally cool temperatures in Europe led to widespread famine and misery, although the connection to volcanic aerosols was not realised at the time.
The Image of the volcano (above) is from the NASA Space Shuttle, showing the 7 kilometre-wide caldera depression formed in 1815. (Image: NASA.)
Vesuvius, the AD 79 eruption, and the local supervolcano
It was not clear at that distance from which mountain the cloud was rising (it was afterwards known to be Vesuvius); its general appearance can best be expressed as being like an umbrella pine, for it rose to a great height on a sort of trunk and then split off into branches, I imagine because it was thrust upwards by the first blast and then left unsupported as the pressure subsided, or else it was borne down by its own weight so that it spread out and gradually dispersed. In places it looked white, elsewhere blotched and dirty, according to the amount of soil and ashes it carried with it.
Part of Pliny the Younger’s description of the eruption column from Vesuvius in AD 79 and its collapse [Allen, G.B. (editor), Selected Letters of Pliny, 1915]
The image shows Vesuvius in eruption in 1944, typical of small-scale explosive events from this volcano that colour our perception of its eruptive behaviour. The small-magnitude AD 79 eruption of Vesuvius, Italy, was violent and destructive because of the Roman towns scattered at it foot. It is highly unlikely that Vesuvius will ever produce a super-eruption, but across the Bay of Naples lies Europe’s only proven super-volcano that erupted in the past 100,000 years (there may be another in the Aegean Sea).
The map left, based on a satellite image of the Neapolitan-Campanian area, shows the area of the Phlegrean Fields (Campi Phlegrei, inside white box), a caldera volcano that produced a super-eruption about 35,000 years ago. This eruption covered large areas of Southern Europe with an ash deposit, as shown on the map below, most derived from pyroclastic flows that spread out over southern Italy and crossed part of the Appenine Mountains. Now many millions of people live in the same area.
Toba, (Sumatra, Indonesia)
Calderas form by collapse of the crust above a large underground reservoir of magma as it is emptied during an eruption. Very roughly, the volume of the caldera reflects the volume of the magma emptied. Thus the bigger the eruption, the larger the caldera. Toba’s output of about 3,000 cubic kilometres of magma represents the second biggest single eruption yet known.
This false-colour Landsat satellite image shows the 45 x 75 kilometre caldera formed by the eruption 74,000 years ago. The southeastern part of the volcano is off the image.
As well as the huge volume of pyroclastic flow deposits, Toba's eruption formed a very widespread ash fall deposit over the equatorial oceans and southern Asia. New scientific reports are published nearly every year about finding Toba's ash fallout further afield, thus our appreciation of the size of the deposit grows.Link to next section, Frequency, locations and sizes of super-eruptions