In the last weeks, several measurements were done at Grimsvötn volcano. They discovered a currently very high output of SO2 gas in the southwest corner of the caldera in Grimsvötn, very close to the eruption sites of 2004 and 2011, a clearly alarming finding: "This is the first time that we measure so much SO2 at a volcano in Iceland that is not in an eruptive phase and its presence is indicative of magma at shallow level", said volcanologist Melissa Anne Pfeffer from the IMO who was among the specialist during the recent measurements. In the area where geothermal activity of the volcano can be detected at the surface, this has also notably increased.
Sulfur dioxide (SO2) is one of the principal volcanic gasses contained in solution in the magma at depth, but released early when magma reaches shallower depths and pressure drops. It can be regarded as one of the most common precursors when volcanoes erupt. [less]

The event, which could have been triggered by normal fluctuations of hydrothermal activity under the ice is expected to be small. The Icelandic Met Office reports maximum discharge rates on the order of magnitude 1000 cubic meters per second, similar to rates during summer ice melt, and expects no damage to occur. The maximum of the flood is expected to be around the end of the week.
A small shallow earthquake swarm, probably as a result of adjustments in the ice mass above the draining lake, has accompanied the flood today. There are no indications that the flood was caused by a volcanic eruption of Grímsvötn volcano. [less]

What is left of the ash plumes that had affected northern Europe is now dissipating and European airspace is again fully open. [less]

While Kevlavik airport on Iceland has resumed operations since yesterday afternoon, a lower level ash plume (at flight level 200, ca. 6 km altitude) has been drifting SE and is now partly over northern Britain, where several flights had to be canceled. (Source: London VAAC) [less]

At the moment, the plume height seems to have decreased from initially 17-18 km (55,000 ft) to 8-12 km (20,-35,000 ft) and is drifting and spreading W and NW, where it is interfering with transatlantic flight routes.
European airspace has so far not been affected and experts think that a repeat of a major disruption of air travel as during last year's Eyafjallajökull eruption is unlikely. [less]

The eruption was preceded by only 15-30 minutes of intense seismic activity and started at around 19h15 pm local time. It created a large eruption plume above the glacier, reaching of 15-20 km height (50-65,000 feet), which is larger than last year's Eyafjallajökull's plume last year and makes it the largest eruption on Iceland since Hekla volcano in 1947.
Iceland review reports that a group of people stayed in a hut on Grímsvötn volcano the night before the eruption, but had left on Saturday 6 hours before the eruption started. The group noticed nothing unusual, but another group that climbed Hrútafellstindar mountain in the southern part of Vatnajökull glacier said they smelled suphur on the morning of 21st May.More than 100 people climbed Öræfajökull volcano, Iceland’s highest peak, on Saturday and saw nothing unusual. [less]

While this might well be caused by heating of the volcano due to rising magma leading to a new eruption, Icelandic volcanologist say that seismicity under the volcano is still low. There are other possible caused that could explain the increase in melt water outflow, such as geomorphical changes in the drainage system allowing an increased discharge of accumulated meltwater on top of the volcano. [less]