(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

An Icelandic volcano was prominently featured in March and April’s news, first for its gentle, tourist-friendly eruptions, and later for its catastrophic ash eruptions that shut down European air traffic for six days. The volcano’s name, Eyjafjallajökull or Eyjafjöll, doesn’t easily roll off anyone’s but Icelander’s tongues.

Iceland, like Hawaii, was created by volcanoes. Iceland is almost 10 times larger in area than Hawaii Island, with twice as many people. In plate tectonic terms, Iceland was created by the coincidence of a hot spot and a spreading plate boundary, whereas Hawaiian volcanoes were produced by a hot spot beneath the middle of a plate, far from the nearest spreading boundary.

Eyjafjallajökull volcano is quite a bit smaller than Kilauea — in length it would span the east rift zone from Puu Oo to Cape Kumukahi — but is a bit taller in elevation. Eyjafjallajökull and its larger neighbor, Katla, are the southernmost volcanoes on the Icelandic mainland. Both have erupted historically.

The March eruption of Eyjafjallajökull volcano started on its eastern flank after months of inflation and heightened seismicity. Lava fountains up to 100m (330 ft) high played along a short fissure and fed thick aa lava flows that advanced only 1.6 km (1 mi) to the north. The longest flow created spectacular lava falls as it dropped through a steep canyon.

Iceland’s initial Hawaiian-style eruption produced an average of about 13 cubic meters of lava per second (206,000 gallons per minute) from its start on the evening of March 20 through a slow-down in activity on April 7. This average was about 3–5 times the typical long-term Kilauea eruption rate but well below that of a typical Mauna Loa eruption. This phase of Eyjafjallajökull’s eruption stopped on April 12, 2010.

Late on April 13, a swarm of small earthquakes began under the central part of Eyjafjallajökull, and an eruption at its ice-capped summit caldera was confirmed April 14.

This activity was much more explosive for two reasons: (1) the magma was more gas-rich than that erupted during the March flank event, and (2) hot lava rapidly melted the overlying ice cap, producing meltwater that flashed explosively into steam.

Cinder and ash were ejected high into the atmosphere and, by April 15, had been blown eastward, resulting in closures of most European airspace. Ingestion of volcanic ash into jet engines can foul critical parts and sensors, which can result in significant loss of power during flight — not a good thing.

About 100,000 flights were cancelled and millions of passengers and cargo containers were stranded during the six-day closure.

Icelanders were, at first, happy about the potential boon to tourism created by the relatively safe flank eruption. The good publicity was welcome, given the bad publicity about the collapse of Iceland’s economy in 2008. But the change in eruption styles eventually resulted in even more negative publicity as Iceland’s ash spread over Europe.

During the first three days of the summit eruption, 10-20 times more lava was erupted than during the earlier flank event (this higher eruption rate was similar to Mauna Loa eruptions).

By the fourth day, the eruption rate had diminished to less than 30 cubic meters per second (480,000 gpm). The threat of more regional ash dispersal will continue until Eyjafjallajökull’s eruption stops as shown by activity in the past few days.

Local effects from its summit eruption were also profound. Lava from the summit craters melted its way beneath glaciers, creating significant flooding. Known as jökullhlaups, these floods covered portions of the coastal plain west of the volcano, destroying roads, bridges, and farm buildings—losses that will be another blow to the Icelandic economy.

While Eyjafjallajökull has already caused many problems, there is even more to worry about. The two most recent eruptions of this volcano were closely associated with more intense eruptions of its larger neighbor, Katla. So far, Katla has shown no signs of activity.

Icelandic volcanological agencies are keeping a very close watch on both volcanoes. Detailed up to date information can be found online at www.earthice.hi.is/page/ies_Eyjafjallajokull_eruption?74, and
an excellent sequence of photographs showing the range of activity described here can be viewed at http://www.earthice.hi.is/page/jardvis_eyjo_myndir