The Lakagígar eruption was a fissure eruption and the largest eruption since the settlement of Iceland and the accompanying lava flow (Eldhraun) was the third largest on earth since the last ice age. Lakagígar (the Laki crater rows) were formed during 1783-1784. Lakagígar are situated in the south of Iceland. The name stems from the central peak in the area, Laki.
Volcanic eruptions arise through three main mechanisms:
1. Gas release under decompression causing magmatic eruptions.
2. Thermal contraction from chilling on contact with water causing phreatomagmatic eruptions.
3. Ejection of entrained particles during steam eruptions causing phreatic eruptions.
A fissure vent is a type 1 eruption with a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels. This type of volcano is usually hard to recognize from the ground and from outer space because it has no central caldera and the surface is mostly flat. The volcano can usually be seen as a crack in the ground or on the ocean floor.
The Lakagígar eruption began on Sunday, June 8, 1783 as a fissure with around 135 craters opened with phreatomagmatic explosions because of the groundwater interacting with the rising basalt magma. Over a few days the eruptions became less explosive and changed into a magmatic eruption, with high rates of lava effusion, ash falls and the stench of sulphur. The system erupted over an 8 month period , pouring out an estimated 14 km3 of basalt, lava and clouds of poisonous compounds.
The consequences for Iceland -known as the Mist Hardships- were catastrophic. An estimated 20-25% of the population died in the famine and fluorine poisoning after the fissure eruptions ceased. Around 80% of sheep, 50% of cattle and 50% of horses died because of dental and skeletal fluorosis from the 8 million tons of hydrogen fluoride that were released.
The weather became very hot, causing severe thunderstorms with large hailstones. The meteorological impact of Laki continued, contributing significantly to several years of extreme weather in Europe.
For more information visit : http://en.wikipedia.org/wiki/Laki
Fissure seen in NE-direction
Fissure seen in SW-direction
Take care!
Lakagígar is an extremely sensitive area. The gravel is very loose and will crumble at the least disturbance. Moss is very delicate, and every footstep leaves a longlasting mark. Please keep to marked trails. This is the best way you can help conserve this magnificent area.
In order to log this earthcache you have mail me the answers of the following questions:
- Standing on top of Laki-mountain, can you determine whether the mountain itself is part or no part of the fissure? Explain your answer.
- What kind of volcanic phenomenon you find at N64 03.908 W18 15.108
Finally, it is appreciated to include in the log a picture of you and your GPS at the top of Laki-mountain at N 64° 04.208 W 018° 14.183 with in the background the craters of the fissure.
SeeExample-log-picture