This month’s stunning image from Earth Science Picture of the Day, taken on 8 September this year is of Iceland’s biggest fissure eruption (video clip) since 1875, in the Holuhraun lava field, which began on 31 August this year. The flow is about to meet the Jokulsa a Fjollum, a large river flowing from Iceland’s largest ice cap Vatnajokull. At the time of writing (29 September) lava is flowing along the river bed at around 1 km each day. So far, the flow has spread over 44 square kilometres, and risks blocking the Jokulsa a Fjollum where it flows through a narrow channel bounded by older lava flows. If that happens the river will form a substantial lake until it is able to flow over and erode the bedrock, and will also leave one of the country’s spectacular waterfalls (Sellfoss) dry.
The fissure is connected to the large Bárðarbunga stratovolcano that lies beneath Vatnajokull, which is currently showing signs of subsidence, at about 40 cm each day, and seismicity. There are concerns that this activity may presage an eruption there which may melt large volumes of ice and perhaps release a flood or jökulhlaup from beneath the icecap. Such a flood would likely follow the course of the Jokulsa a Fjollum river.