Volcanic Activity – Increasing Seismic Unrest at Mýrdalsjökull Glacier: Katla Volcano, Iceland
Europe – Iceland | Southern Iceland, Mýrdalsjökull Glacier, Katla Volcano
Location: 63°37’58.8″N 19°04’58.8″W
Subglacial volcano: 1.512 m (4,961 ft)
Current status: Unrest
Eruption Type: Explosive basaltic and dacitic eruptions, voluminous lava flows
Warning: Glacial water is flowing into Múlakvísl river, south of Mýrdalsjökull. Increased conductivity has been measured in the river and gas measurements in the area show high concentrations of sulfur dioxide and hydrogen sulfide. More
Katla volcano (Iceland): magnitude 4.5 earthquake, strongest in decades
Volcano Discovery Update Monday, 29 Aug 09:43
At least one earthquake of magnitude 4.5 occurred this morning under the volcano, the strongest recorded for Katla in recent decades. It was felt in nearby areas.
The Icelandic Met Office (IMO) reported two quakes, one at 01:47:02 local time at 3.8 km depth 8.1 km east of the summit (Goðabunga) followed 20 seconds later by another magnitude 4.5 quake at 0.1 km depth. Caution is required as these data are from automatic calculations which could actually in fact describe only one quake.
During the past 48 hours, IMO has detected 48 earthquakes – most of them tiny, but including 4 of magnitudes of 3 or higher – at shallow depths under Katla.
Whether these earthquakes are caused by magmatic activity – and thus could be a sign of a new eruption in preparation – or a result of gravitational adjustments (as ice melt during the summer changes the weight of the glacier) is currently unknown.
Colors indicate the timing of epicenters and their respective plotted magnitudes, recorded as late as 2250 on 9 July 2011, according to the scheme shown below the map. Black triangles indicate seismic monitoring stations.
On the micro-earthquake activity at Mýrdalsjökull – Monitoring statement with regard to the Katla volcano
The following summary by the Icelandic Meteorological Office is about a recent increase in earthquake activity at the ice-covered Katla volcano, Iceland. Media interest in Iceland’s volcanoes has remained high since the Eyjafjallajökull eruption of 2010, hence the summary is intended as an official monitoring statement, in case of diverging media reports.
Since mid-June, earthquake activity within the caldera of the ice-covered Katla volcano has increased above background levels. More than 100 shallow-seated earthquakes have been detected in Katla caldera since 1 June 2016, which is almost four times the monthly average compared to previous years. Earthquakes occurred mainly in bursts ranging from minutes to hours, often with 20 events or more. The two largest earthquakes since the unrest began occurred on 26 July at 03:42 and 03:50 UTC, respectively, both with a magnitude of Mw3.2.
Such summertime increases in seismicity are common at Katla and the ongoing activity within the caldera is similar to summertime unrest observed in 2012 and 2014. Often this increased seismicity occurred in association with drainage of meltwater from several known ice-cauldrons, formed due to hydrothermal activity, as observed almost annually. Since late June 2016 there have been three small floods in Múlakvísl river, an outlet from Mýrdalsjökull, in addition to a flood from the Entujökull glacier. Presently, water-level and electrical conductivity measurements at the bridge over Múlakvísl show increased drainage of geothermal meltwater from Mýrdalsjökull – the ice-cap overlying Katla. We have received several reports throughout the summer of a hydrogen sulphide stench from glacial rivers around Myrdalsjökull.
Around Katla we are not detecting signs of increased ground deformation or bursts of seismic tremor, which are both signals that might indicate movement of magma. We continue to monitor Katla closely and will issue updates on IMO‘s web-site if the situation intensifies. Our assessment is that the volcano is in a period of summertime unrest and it does not show signs of impending eruption, although we cannot rule-out a sudden escalation in seismicity in connection with a hazardous flood.
On-line overview of seismicity levels within the caldera is available.
An overview of the Katla volcanic system is given in the Catalogue of Icelandic Volcanoes.