Kárahnjúkar Dam and Hálslón Reservoir
About Kárahnjúkar Dam and Hálslón Reservoir
Kárahnjúkar is the site of Iceland's largest dam, in the eastern highlands north of Vatnajökull, where a wall of rock and concrete blocks the glacial river Jökulsá á Dal to form the Hálslón reservoir. The main dam rises up to 198 meters and runs 700 meters across the head of a deep canyon, and the paved road that crosses its crest makes the dam one of the few highland sights you can reach without a 4x4.
Hálslón covers about 63 square kilometers when full and stretches 25 kilometers south toward the ice cap. Its milky, silt-heavy water feeds a 40-kilometer tunnel that runs through the mountains to the underground Fljótsdalur power station, which supplies the aluminum smelter at Reyðarfjörður. Building it was one of the most disputed projects in modern Iceland, and the debate over the land it flooded still comes up today.
In late summer, once the reservoir is full at 625 meters above sea level, the overflow pours down a spillway on the western side of the dam. The result is Hverfandi, a temporary waterfall that thunders into the Hafrahvammagljúfur canyon below and usually runs from around August into fall. Downstream, the reduced flow in the river is also what uncovered the basalt columns at Stuðlagil.
Getting to Kárahnjúkar takes about an hour and a half from Egilsstaðir, roughly 97 kilometers, most of it on Road 910, which climbs out of Fljótsdalur, the valley of Hengifoss and Skriðuklaustur, onto the plateau. The road is paved all the way to the dam, but it is a highland road with no services, so fill up and pack food before you leave the valley.
Visit Kárahnjúkar between July and September, when the highland road is reliably clear of snow. Late August and September give you the best chance of seeing Hverfandi, and the same trip can continue to Snæfell if you have a 4x4. Expect cold wind on the dam even in summer, since the crest sits more than 600 meters above sea level.
Good to know
Where is the Kárahnjúkar dam?
Kárahnjúkar dam is in the eastern highlands of Iceland, north of Vatnajökull, about 97 kilometers by road from Egilsstaðir. It blocks the river Jökulsá á Dal to form the Hálslón reservoir.
How high is the Kárahnjúkar dam?
The main dam is up to 198 meters high and 700 meters long, making it the largest dam in Iceland. Two smaller side dams help hold the reservoir in place.
Can you drive to Kárahnjúkar without a 4x4?
Yes. Road 910 is paved all the way from Fljótsdalur to the dam, so a regular car can make it in summer. Check the road conditions map first, as snow can close the highland road outside the summer months.
What is Hverfandi waterfall?
Hverfandi is a temporary waterfall that forms when the full Hálslón reservoir overflows down the dam's spillway into Hafrahvammagljúfur canyon. It usually appears in late summer and can run into fall.
How big is Hálslón reservoir?
Hálslón covers about 63 square kilometers at full supply level and is 25 kilometers long. It fills with glacial meltwater over the summer and reaches its top level of 625 meters above sea level in late summer.
How long does it take to drive from Egilsstaðir to Kárahnjúkar?
Allow about an hour and a half each way for the roughly 97-kilometer drive, mostly on Road 910. There are no services at the dam, so bring food and fuel.
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