A very long, but very small, eruption
The Hekla eruption of 1947-48 was longer than the current eruption, as was Surtsey in 1963-67, and Krafla in 1975-84. During the same time, only Askja (1961), Hekla (1981), and Fimmvörðuháls (2010) have produced less lava than Fagradalsfjall/Geldingadalir. The power of this year’s eruption was also generally low, according to University of Iceland geology professor Sigurður Steinþórsson, writing on Vísindavefurinn.
"The most powerful eruptions on the list are, on the one hand, the great effusive eruptions, Skaftáreldar 1783-84 and Holuhraun 2014-15, and on the other, explosive eruptions, either pure (Hekla 1980) or with “short effusive eruption periods” (Hekla 1991 and 2000) — the explosive part of Hekla 1947 was extremely powerful but it was accompanied by lengthy lava flow,” the article states.
Sigurður registers the eruption as finishing on 18th September this year, even though this is not yet official.
Since then, no magma has emerged from the crater. However, there has been flow within the lava field, and west of the crater, north of Geldingadalur, it has subsided by five-to-seven metres. The displacement explains the molten glow that has occasionally been seen in the lava. Displacement of this kind is not uncommon in lava eruptions. The lava field is made up of 150 million cubic metres of lava, covering 4.85 square kilometres.