Katla Volcano in Iceland

Katla is an active volcano beneath the Mýrdalsjökull ice cap on Iceland's South Coast, north of the village of Vík. Glacial ice up to 700 m (2,300 ft) deep fills its caldera, so Katla volcano has no summit, crater, or slopes you can see. The last eruption to break through that cover came in 1918. One of the most closely monitored volcanoes in the country, ten seismic stations surround it, feeding the Icelandic Meteorological Office around the clock. Automatic warnings trigger when activity increases.

The view from the road is as close as most visitors get. Going onto the ice takes a guide.

Katla is a subglacial central volcano, so the mountain itself lies under a glacier instead of above it. Its summit holds a caldera, a wide basin left behind when a volcano's roof collapses into the emptying magma chamber below. Mýrdalsjökull fills that basin with hundreds of meters of ice.

Magma rising inside the Katla caldera has to melt its way out first. Meltwater reaching that magma flashes to steam, shatters it into fine ash, and drives an explosive column upward. The water escapes as a jökulhlaup, a glacial outburst flood that these eruptions are known for. At their peak, these floods carry up to the order of 300,000 m³/s (10.6 million ft³/s), more than the Amazon's average flow into the Atlantic.

Katla's largest eruptions happened beyond the ice cap altogether, along its fissure swarm, a band of long ground cracks reaching about 70 km (43 mi) northeast. With no ice overhead, the magma spreads as lava instead of ash. The Eldgjá fissure system in that band erupted around 939 CE. The eruption produced roughly 20 km³ (4.8 mi³) of lava and tephra, meaning fragments of rock blown into the air. The flow ranks among the largest known on Earth.

Katla owes most of its international profile to Eyjafjallajökull, its neighbor 25 km (16 mi) to the west. When it erupted in 2010, the ash cloud shut more than 300 airports in roughly two dozen European countries. A few previous Eyjafjallajökull eruptions were followed by a Katla eruption within two years. The two appear to be connected underground, so scientists watched closely through 2010 and added more sensors around the ice cap.

Only three of Katla's recorded eruptions came after an Eyjafjallajökull event. The 2010 event broke the sequence. What keeps Katla under watch is its own behavior. Earthquake activity below the ice stays high and steady even in quiet years, which is unusual among Icelandic volcanoes.

Yes, Katla is an active volcano. Active describes what a volcano has done and can still do, not a warning that something is imminent. Katla will erupt again at some point, although the Icelandic Meteorological Office says the timing is difficult to forecast.

Recent activity has produced meltwater, not lava. Possible small eruptions under the ice in 1955 and 1999 never broke the surface. The disruption has come from floods: one in July 2011 destroyed the bridge over the Múlakvísl river on Route 1. Another in July 2024 washed out a stretch of road further east. IMO attributes floods like these to geothermal heat that melts the base of the glacier, pooling water that collects and then breaks out.

If a hazard assessment shows increased threat, Civil Protection moves up a three-stage scale. At the middle stage, hættustig, authorities can impose restrictions, close roads, and evacuate or relocate residents. A response plan written specifically for a Katla eruption already exists, so nobody needs an app to be warned. Every capable phone receives alerts inside the affected area through the cell network.

Katla has erupted at least 21 times in the past 1,100 years, most recently in 1918. The eruption began on Saturday, 12 October, and the flood reached the sea within 45 minutes of leaving the glacier. Most of the water spread over Mýrdalssandur, the black-sand plain east of the volcano that Route 1 now crosses. Flooding continued for two weeks, and smaller bursts followed for another two after that.

The flood dumped enough sand and ash at the coast to push the shoreline south and build a new point of land, Kötlutangi. Until then, Dyrhólaey had been Iceland's southernmost mainland point. The sea started taking Kötlutangi back almost at once. After big storms, the 1918 layer still shows on the beach.

Katla lies under Mýrdalsjökull in the far south of the country, with Eyjafjallajökull to the west and Vík í Mýrdal on the coast to the south. Vík is the country’s southernmost village and the nearest place to base yourself. The drive from Reykjavík takes about 2 hours and 40 minutes. Both the volcano and Vík are inside Katla UNESCO Global Geopark, which covers around 9% of the country.

Route 1 takes you along the South Coast from Reykjavík to Vík, which is where the glacier trips start. East of Skógar, this drive follows the foot of Mýrdalsjökull, crossing sand plains and glacial rivers. The final stretch from Vík to the ice lasts about 30 minutes.

The Ring Road is paved the whole way and needs nothing more than a normal car. The tracks inland are unpaved, and mountain roads open only once the snow clears. Driving off marked roads is illegal anywhere in Iceland, so there's no improvising your way closer.

Not in the way most people expect. Katla is buried, so there's nothing to hike up and no viewpoint that shows you a volcano. From Route 1, you see the ice cap on the skyline, the outlet glaciers coming off its edges, and the black sand plains its floods left.

Reaching the ice takes a guide and a Super Jeep on oversized tires, because the route leaves the pavement. Official safety guidance warns against going onto any glacier without experience and proper equipment. Guided glacier tours in the Katla area go onto Kötlujökull.

Mýrdalsjökull is the glacier over Katla. Kötlujökull is the outlet glacier flowing southeast off its edge. Mýrdalsjökull covered 520 km² (201 mi²) in 2019, making it Iceland's fourth-largest. Like every glacier in the country, it’s been shrinking since the late 1800s.

The black streaks in the ice are old volcanic ash. Each eruption drops a layer on the surface, and later snowfall buries it deeper year by year. The glacier slowly carries those layers downhill, and melting near the front exposes them again as dark bands.

The South Coast is open year-round, and the season changes what the drive is like more than what you can see. Summer brings near-endless daylight and easy driving on clear roads. Winter cuts daylight to a few hours, and snow covers the ice cap and the sand plains. Storms shut Route 1 from time to time. Spring and autumn are quieter on the road and in the parking areas.

Weather here turns fast in any month, so check road conditions before you set out, and safetravel.is carries current alerts.

All of these lie in the same Geopark as the volcano:

• Glaciers and ice: Sólheimajökull is an 11 km (7 mi) outlet glacier off the southwest side of the ice cap, and its snout has been measured every year since 1930. A lagoon started forming in front of it in 2011 and is now 60 m (197 ft) deep.
• Coast: Reynisfjara lies between Dyrhólaey and Mount Reynisfjall, backed by basalt columns. The surf here is unpredictable even on calm days, so stay above the wet sand line and follow the warning lights. Dyrhólaey is named for the arch the sea cut through the headland, wide enough for a boat to pass through in calm conditions. The mudflats of the Dyrhólaós lagoon behind it feed migrating birds crossing between mainland Europe and Greenland.
• Waterfalls: Skógafoss drops 60 m (197 ft) and is the last fall on the Skógá before the river reaches the sea. Seljalandsfoss is the same height and a path leads behind the falls, though ice makes it dangerous in winter. Gljúfrabúi stands in a cleft alongside, with only its top visible from outside.
• Hiking: the Fimmvörðuháls trail leaves Skógar, follows the Skógá up between Eyjafjallajökull and Mýrdalsjökull, and crosses the pass to Þórsmörk.
• Villages: Vík grew up as a trading and service point for the surrounding farms and is Iceland's only seaside settlement without a harbor. The Katla Center in the old Brydebúð building is the Geopark's visitor hub, with exhibitions on the volcano, its eruptions, and its floods.