The recent volcanic eruption of Mount Eyjafjallajökull in Iceland has once again brought home the effect that volcanoes can have on society, even in a technologically-advanced society. The ash plume from the eruption reached as high as 7km into the air, and the glass-rich ash caused major disruptions in air travel.
As volcanoes go, Eyjafjallajökull is a relatively small one, and its influence likely to be short-lived. It’s devastating effects on air travel were more of the “right-place, right-time” variety, rather than the power of this particular volcano. Not only does Iceland lie right along the major routes between North America and Europe, but prevailing winds carried the clouds of ash right over Europe. Estimates run as high as 100,000 fights cancelled, the worst economic disaster to befall the airline industry, ever.
Other volcanoes, some in the fairly recent past, have done more to illustrate just what a volcano can do, both regionally and to the global climatic system. Mount St. Helens, of course, provided a vivid example for North Americans, used to hearing about earthquakes and volcanoes happening “somewhere else”. Mount St. Helens blew its top right off, and devastated 600 square kilometers of forest and buildings, blocked rivers, and resulted in localized flooding along the Columbia River. The death toll from the actual eruption was only 57, as scientists and authorities had plenty of warning that the mountain was set to erupt.
Mount Pinatubo, in the Phillipines, provided less warning, and killed over 800 people when it blew in 1991. However, the millions of tons of ash and dust it threw up into the atmosphere caused longer-term effects over the entire globe. All of this ejecta floating through the air blocked a small but significant amount of sunlight. Temperatures fell 0.5 degrees across the planet, and caused some localized crop disruptions and failures.
Likewise, the explosion of Mount Krakatoa in Indonesia, in 1883 could be heard over 5000 km away, and the amount of dust and ash kicked up by that saw world-wide temperatures drop by 1.2 degrees Celsius. Weather patterns were disrupted for years afterwards, and did not settle down into any degree of normalcy until 1888.
Of course, in addition to these global effects, volcanoes can have severe localized effects, including poisoning the ground and water supply. Animals suffer severely as well, with the Mount St. Helens eruption estimated to have killed over 7000 large wildlife, including moose and deer, while at Mt. Pinatubo hundreds of thousands of livestock were killed.
Flooding can result from lava flows and landslides caused by displacement of material from the volcano.
Over time, however, both local and global systems adjust and normalize. This should give us hope that, once we get our own emissions under control, that the global climate, too, will adjust and settle back down.