HEKLA MOUNTAIN - VOLCANO
1491-m-high Hekla is one of Iceland's most prominent, most known and active volcanoes. It has frequent eruptions that start with an explosive onset producing eruption plumes, then lava fountains and culminate in large lava flows. Most of the volcano's flanks are covered by extensive lava flows from historical eruptions, dating back to 1104 AD.Hekla is located near the southern end of the eastern rift zone. It sits on a rift-transform junction, and has produced basaltic andesites, in contrast to the tholeiitic basalts typical of Icelandic rift zone volcanoes. Hekla's tephras are generally rich in flourine, which is very hazardous to grazing animals.
The elongated shape of the volcano is caused by a 5.5-km-long fissure, Heklugjá, that cuts across the volcano and is often active along its full length during major eruptions. Repeated such eruptions, oblique to most rifting structures in the eastern volcanic zone, have created Hekla's elongated ENE-WSW profile.
Frequent large explosive eruptions during historical times have deposited tephra throughout Iceland and provide important time markers that can be used to date eruptions from other volcanoes in Iceland.
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EYJAFJALLAJÖKULL - VOLCANO
Situated in the south of Iceland, Eyjafjallajökull is an 800,000 year old volcano and is reckoned to be the oldest active strato volcano on the island. By comparison, Hekla is a mere infant at just 8800 years of age.
Ice-capped Eyjafjallajökull (the name is made up of three parts: eyja = island, fjall = mountain and jökull = glacier) is topped by a crater, whose rim rises to 1666 metres in height from the coast, which is just a few kilometres from its base. Shrouding the volcano is an ice field 75 km² in area and 50-200 metres thick but thicker in the summit crater, from where Gígjökull (crater glacier) drops over 1000m in a steep and deeply crevassed icefall to the valley floor north of the volcano. By all standards it is a beautiful and shapely volcanic cone, a landmark visible from afar that is made all the more impressive by its glaciers.
Eyjafjallajökull normally stays out of the limelight and is less known and less active than other Icelandic volcanoes, its last eruption occurring in 1821-23. Perhaps this is because historically Icelanders have been much more in awe and fear of its powerful neighbour, Katla, whose eruptions at roughly 50 year intervals under Mýrdalsjökull, a much larger and thicker icecap, provoke widespread flooding on the coastal plains. But, what made the Icelanders jittery on this occasion is that Katla is long overdue and can be triggered by activity on Eyjafjallajökull. Katla last blew in 1918 provoking a flash flood of 200,000 cubic metres of muddy, swirling melt water per second – to give you an idea of the scale of it that's twice the average flow of the Amazon at its mouth. Icebergs the size of houses were seen floating at sea.
Luckily Katla, which has erupted 20 times in the last 1200 years, is currently simmering on the back boiler. The past decade has seen swelling and red alerts from time to time though there is practically no seismic activity under the volcano at present. Katla is closely monitored by scientists. In their expert opinion there is no indication of an eruption since there is no movement in sites to the west and east of the glacier Mýrdalsjökull. Eyjafjallajökull and Katla are two separate volcanoes – with two separate magma chambers – and are not connected as such.