#grimsvotn

The remnants of Laki

In 1783, a volcanic eruption known as Laki took place in Iceland’s eastern volcanic zone. This event was mostly a fissure eruption: it took place in a series of fractures or “fissures” that extend outward from the Grímsvötn magmatic system that is likely the largest in Iceland. This chain of craters marks the locations where the lavas poured out, a line 23 kilometers long.

After an early series of earthquakes related to the movement of magma, the ground split open and huge amounts of lava poured out. The lava cascaded over Iceland, burning its way from the high ground near its source down towards the coastline.

The amount of lava produced in this eruption is staggering. Most of the lava erupted in about the first one and a half months, and the volume erupted during the full eruption is about 3.5 times the amount of lava that has erupted from Kilauea during the Pu’u O’o eruption, which has continued almost without interruption sine 1983. More than 30 years of Kilauea, multiplied by 4, erupted within a couple months.

This eruption had impacts throughout the world. The plume of gases released by the eruption headed out over Europe, causing severe climate issues, famines, and maybe even helping drive the French Revolution a few years later.

-JBB

Image credit: http://commons.wikimedia.org/wiki/File:Laki_Iceland_East.JPG

A single lightning bolt climbs the ash cloud of erupting Grímsvötn volcano in Iceland.

Grímsvötn: volcán más activo de Islandia estaría a punto de hacer erupción

Se trata del volcán más activo de Islandia, y con un nombre un poco complicado de pronunciar (Grímsvötn), este coloso ahora amenaza con hacer erupción.

Hekla, Eyjafjallajokull, Grimsvotn, and Laki.

These are the Fab Four of Icelandic volcanoes. The picture is of Eyjafjallajokull. Looks benign doesn’t it?

Travelling along the Ring Road near Skogar on Iceland’s southern coast is a birdwatcher’s delight. Arctic terns fly along the fences by the road, oystercatchers in flocks of between 5 and 13 hunt on foot in the fields around two miles from the sea, and whimbrels sit on the fence posts…

Jokulhlaup: When fire meets ice.

Some of the most spectacular floods on Earth burst out when a volcano erupts under an icecap or glacier. This happens frequently in Iceland, where Grimsvotn volcano under Vatnajokul icecap was the type location for this phenomenon. Also known as glacial volcanic outburst floods, they can be very destructive, releasing huge volumes of water in a very short time, which can also mix with ash on the surface to become lahars. These resemble a fast flowing thick river of mud, their destructive power magnified by its higher density, often incorporating boulders, trees and floating ice blocks the size of houses. The rock formed by these eruptions resemble those formed under water, with pillow lavas and hyaloclastite (a sand sized sediment formed of shards of volcanic glass spalled off by steam when lava meets water).

Grimsvotn is one of the world's more active volcanoes, with over two dozen eruptions in the thousand or so years of Iceland's Viking history. A huge glacier-filled caldera sitting on the mid-Atlantic rift, its magmatic plumbing is connected to the same system that produced the devastating Laki fissure eruption in 1783 (see out previous post at http://tinyurl.com/ot75tq8). The magma melts the ice, an a permanent warm lake exists at the bottom of the glacier, whose level is closely monitored by volcano hazard specialists. When an eruption happens, the glacier melts and the lake level rises as the glacier sags above it, until the hydrostatic pressure exceeds the ice overburden pressure and the water wedges the glacier up from the underlying rock and travels beneath it to explode out at its edge.

In the 1996 eruption 500000 cubic metres of ice were melted every day, and when the flood burst out, its discharge rate was 45000 cubic metres a second. Bridges and power lined were destroyed, but Iceland's long experience with these events mean that their usual paths are known and therefore sparsely inhabited. The lahars added several square kilometres to Iceland's coast. In 2003, the pressure release as the lake drained caused an explosive eruption, which sent ash columns into the air, forcing the diversion of aircraft from Iceland's busy air lanes (these lanes over oceans are routed to stay within the closest reach of airports along the way in case of emergency, and the routes between the US East coast and Europe all criss cross near Iceland). The time taken for the water to travel to the ice's edge is either very fast (2-3 days), when the whole cap is lifted, or slow (up to 2-3 weeks) when the water melts channels more gradually through the ice.

The 1967-70 eruption at Deception Island in Antarctica forced evacuation of a research base which was destroyed soon after by a jokulhlaup.

On another note, this word is one of my favourites in the geological language, sounding like something from the Norse legends. To an English ear it rolls off the tongue in a surreal but not dissonant way, with a pleasing sounding rhythm. Do our readers have any favourite sounding geological terms of their own to share with us? Entries we like will get an official TES like to cherish, and may even see them turn up as a post.

Loz