- Written by Nadia O’Carroll
There have been many notable volcanic eruptions that have had significant effects on human history. In the Bronze Age, an eruption in the islands of Santorini in the Aegean Sea destroyed the Minoan civilisation and gave rise to the legend of Atlantis. In approximately 180 AD, Taupo in New Zealand erupted so violently that fiery red skies produced by its ash were recorded in China and Rome. The eruption of Mt Tambora in Indonesia in 1815 produced so much ash and sulphur dioxide that sunlight was filtered out and world wide weather patterns were disrupted, as a consequence in the Northern Hemisphere, 1816 was called the year without a summer. A cataclysmic eruption in the island of Krakatoa in 1883 blew two thirds of the island (21 cu kms) into the atmosphere, the sound of the blast could be heard in Perth, the magnitude of energy released by the blast was estimated at 200 megaton of TNT (as a comparison the Hiroshima atomic bomb was about 20 kilotons of TNT) and tsunamis of up to 40 metres were produced.
The most significant eruption for humans predates recorded history. The Toba supereruption occurred in Indonesia approximately 74,000 years ago. This was an eruption of catastrophic proportions, which produced major ecological and climatic change throughout the world. It is estimated that only 10,000 humans survived the impacts of this supervolcano . There is a theory that this catastrophe produced a genetic bottleneck in human evolution, which caused the low numbers of humans surviving in isolated refuges to differentiate abruptly into modern races.
The basic reason volcanoes occur is that pressurised molten rock (magma) erupts through a weak point in the Earth’s surface. Gases, debris, magma and ash are projected through the rupture.
These weak spots are a result of three main types of geological activity. Tectonic plates are huge slabs of the Earth’s crust which are rigid but float on the hotter softer layer of the Earth’s mantle, these plates move continuously and independently. If the plates are sliding along beside each other the surface is stable, but if the plates are pulling apart (diverging) or pushing together (converging) then weak spots in the surface are created. This is why boundaries of tectonic plates experience volcanoes and earthquakes, the most active being the Pacific Rim of Fire. Volcanoes can also be found away from tectonic plate boundaries at hotspots where the surface is stretched or thin.
The Earth’s largest volcanoes, such as the Tweed Volcano, predate humans. The plateau of Tamborine Mountain is actually the northern limit of a vast dome of lava produced by this ancient colossus twenty million years ago.
Fortunately for us the Tweed Volcano is well and truly extinct.