Eruption frequency
Every 5–10 years
Most frequently erupting volcano in Iceland.
Grímsvötn: Iceland's Most Frequently Erupting Volcano
Iceland's most frequently erupting volcano, buried beneath the Vatnajökull ice cap and a major source of jökulhlaup glacial floods and ash plumes.
Region
Under Vatnajökull
Not accessible. Monitored remotely by IMO.
Quick Answer
Beneath the Vatnajökull ice cap, Grímsvötn is Iceland's most frequently erupting volcano. Its geothermal heat melts ice from below into a subglacial lake that periodically bursts out in catastrophic floods. The 2011 eruption produced a 20 km ash plume and temporarily disrupted flights across northern Europe.
A glacial flood does not necessarily mean an eruption
A jökulhlaup is an outburst of stored water. At Grímsvötn it can happen without a volcanic eruption: in its January 2024 flood report, the IMO counted twelve floods since 2004 that had not triggered volcanic activity. Conversely, the 2011 eruption was not preceded by a flood. Those observations explain why a flood headline and an eruption warning should not be treated as interchangeable.
For a Ring Road trip, the relevant question is whether water is affecting the rivers and roads across Skeiðarársandur. Read the date and named river in an IMO bulletin, then check road notices for your route. The conclusion of a historic flood is not evidence that the road is open today.
Sources and page update
Updated: 2026-09-10
A flood and an eruption are different events. Read the latest dated IMO assessment and road notices before travel across the outwash plain.
For sourcing standards and how to report an error, see the editorial policy.
Last eruption
2011
20 km ash plume, flight disruptions in Europe.
Location
Under Vatnajökull
Subglacial caldera in southeast Iceland.
Key Facts About Grímsvötn
- Subglacial caldera volcano: buried under 200-300 m of Vatnajokull ice; caldera ~10 km across
- Recent eruptions include 1998, 2004 and 2011; the interval varies and does not forecast the next eruption
- 2011 eruption (VEI 4): 20 km ash plume, largest Grimsvotn eruption in a century, brief flight disruptions
- The 1996 Gjálp eruption melted ice; water accumulated in Grímsvötn before a major flood damaged bridges across Skeiðarársandur
- Subglacial geothermal lake accumulates meltwater until it lifts the ice dam and drains catastrophically
- Periodic jokulhlaup floods cross Skeidararsandur outwash plain; twisted bridge remnants still visible
- IMO monitors continuously via seismometers, GPS, and satellite; subglacial lake level tracked closely
Related Areas
- Skeiðarársandur outwash plain
- Vatnajökull National Park
- Skaftafell area and glacier tongues
- Jökulsárlón glacier lagoon
- Svínafellsjökull glacier tongue
- Twisted bridge remains from 1996 jökulhlaup
How to Get There
- Grímsvötn is in the interior of Vatnajökull; this page does not provide a glacier-expedition route
- The closest viewable evidence is Skeidararsandur outwash plain on Route 1 between Skaftafell and Vik
- Twisted bridge remnants from the 1996 jokulhlaup are displayed as a monument off Route 1
- Skaftafell visitor center in Vatnajokull National Park provides information about Grimsvotn and subglacial volcanism
- The marked land-based S1 trail at Skaftafell provides a glacier view; it is separate from an on-ice activity
- Do not treat a glacier tour near Skaftafell as a visit to Grímsvötn; check the exact location of any proposed activity
Best Time to Visit the Area
- Check Route 1 conditions and flood notices for the day; a main road can still close
- June to September: best conditions for Skaftafell hiking and glacier tongue walks
- Jokulhlaup evidence on Skeidararsandur is visible any time of year from Route 1
- Summer: Vatnajokull National Park visitor center at Skaftafell has extended hours and ranger programs
- Winter: glacier tours still run from Skaftafell area; ice formations and northern lights possible
- Read dated IMO volcano and flood notices; historic intervals do not predict the next event
Planning help
Grímsvötn FAQs
Quick answers with safety notes where it matters.
How often does Grímsvötn erupt?
Grímsvötn has erupted frequently in historical times. The IMO lists recent eruptions in 1998, 2004 and May 2011; an average interval is not a countdown to the next one. Its 2011 eruption was substantially larger than the other recent eruptions.
Can you visit Grímsvötn?
Grímsvötn is located under the Vatnajökull ice cap and is not accessible to regular visitors. The caldera is buried beneath hundreds of meters of ice in one of Iceland's most remote areas.
What are jökulhlaups from Grímsvötn?
Grímsvötn's geothermal heat melts ice to form a subglacial lake that periodically drains catastrophically. The resulting floods (jökulhlaups) run down the Skeiðará river and across the Skeiðarársandur outwash plain.
What happened during the 2011 eruption?
The May 2011 eruption sent an ash plume 20 km into the atmosphere and caused temporary flight disruptions in northern Europe. It was significantly more powerful than the 2004 eruption but shorter-lived.
How is Grímsvötn monitored?
The Icelandic Meteorological Office monitors Grímsvötn using several kinds of measurements. A draining lake or increased earthquakes require interpretation; neither alone establishes that an eruption has begun. The IMO notes that warning times can be short.
For a countrywide view of Iceland’s volcanic systems, explore our Iceland statistics.