Icelandic volcanoes have been associated with many devastating impacts, not only for the people of Iceland. Volcanic hazards tend to extend beyond Icelandic soil and travel to the opposite side of the globe, and are therefore considered worldwide hazards. This shows us that although the eruption occurred on land, the nature and volume of eruptions at mid-ocean ridges are very widespread. An example, of a volcano causing detrimental effects on a large scale was the Laki eruption of Iceland in June of 1783. There were over 1000 people that died which accounts for 25% of the population, and about half of the islands cattle and three-fourths of its sheep died. Furthermore, a large number of hectares and vegetation also perished.
A great number of people and livestock died from suffocation caused by the pyroclastic flow- the most dangerous feature of volcanoes. The pyroclastic flow is extremely hot and triggers high velocity winds (exceeding wind speeds in hurricanes) within the cloud and the poisonous volatile gases which are capable of destroying all life within many miles of the volcano in a matter of minutes**. These gases include sulfur dioxide (SO2) and sulfur trioxide (SO3) which are poisonous alone, however combined with water from sulfuric acid (HCl), carbon monoxide (CO), hydrofluoric acid (HF) and boric acid (H3BO3) can kill within a matter of minutes once inhaled.
People and livestock also died due to the secondary effects. The islands vegetation rapidly perished under a blanket of ash. This vegetation could not receive any sunlight to flourish as the ash which coated it blocked the sunlight. Due to a lack of vegetation widespread famine traveled across Europe and diseases surfaced due to the lack of nutrition, effecting the livestock and human inhabitants of the island. Furthermore, the haze that coverers the sky after an eruption, results from the sulfur gases reacting with water vapor, this blocks the suns rays and is therefore detrimental to both life on land and in the ocean. Volcano Laki efficiently eliminated the 1783 summer and it was the coldest in 500 years in some locations, according to tree ring data. The sun was obscured by the vast cloud caused by the Laki eruption and, what should have been a warm summer in the northern hemisphere, took on winter proportions, not just in Iceland, but all over Europe.** Poems were written that included descriptions of the sun- ‘pale blood red ghost within the volcanic haze. ‘In reference to the laki volcano in Iceland, Benjamin Franklin during a lecture in 1784 made the following comments’, when the effect of the sun’s rays to heat the earth in these northern regions should have been greater, there existed a constant fog all over Europe, and a great part of North America…’this haze was also observed over Asia and North Africa. These days the haze would cease aviation over much of Europe if an eruption the capacity of Laki occurred. The haze does not only decrease visibility, but it also damages aircraft. For example, the most common result is engine damage that occurs when volcanic ash enters the jet intakes; the volcanic ash melts and cools to become glass coating the turbine blades, often causing the engines to stall.
Further secondary effects included contaminated water supplies within Iceland. The water became poison due to its contact with pyroclastic flow and being supplied with acid rain. A build up of fluoride within the drinking water caused ‘fluoride poisoning’ which resulted in bone deformities in people and livestock evident in graveyard excavations.
Volcanoes also have the capacity to interrupt the normal weather patterns not only locally, but also on a large scale. For example, in France the extreme weather resulted in a surplus harvest in 1785 that inflicted poverty upon rural workers, accompanied by droughts, bad winters and summers, involved a horrific thunderstorm and hailstorm in 1788 that damaged crops. This in turn contributed significantly to the build up of poverty and famine that triggered the French revolution in 1780. Recent computer modeling shows that the cooler temperatures in the Northern hemisphere in 1783 caused a weak monsoon for Southern Asia and Northern Africa. The unusual cold in the North lessened the temperature contrast between the land and the oceans, upon which the monsoon winds rely for their development and strength. With little or no monsoon, there are no clouds to produce rain for rivers or to prevent the surface evaporation. Without rain there was no irrigation supplied for crops and this resulted in a food shortage for these countries. The cooler weather also caused the Mississippi River to freeze and the formation of ice in the Gulf of Mexico. These unprecedented weather patterns upon Europe continued for several years
Lava is another dangerous feature of volcanoes. The vent of the Laki volcano was marked by a row of lava fountains throwing red-hot molten basalt tens of meters into the air and in a single day, the front of the lava flow advanced 15km2, making it the largest historic eruption. The destructive power of lava flows lies in the high temperature of the rock, which can set structures aflame, and in the size and mass of the flow, which can engulf or crush even large buildings. One observer of the Laki volcano said ‘all the earth’s plants burned, withered and turned gray, one after another, as the fire increased and neared the settlements.’
Earthquakes can also be triggered by volcanic activity. The Earthquakes are produced by stress changes in solid rock caused by the insertion and/or removal of magma. These earthquakes can cause land to subside and can produce large ground cracks**. Furthermore, the Laki eruption was heralded by a series of earthquakes and the opening of fissures 25km long, and a shallow graben formed between two of the fissures.