Iceland Mag

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Iceland Mag


Why are geothermal ice caves dangerous? What is known of the cave where a hiker died yesterday?

By Staff

  • Inside the cave The cave in Blágnípujökull glacier, an outlet glacier of Hofsjökull. Photo/Screenshot from video, see below.

The tragic accident in a ice cave in Hofsjökull glacier, where a hiker was found dead shortly before midnight on Wednesday February 28, reminds us that ice caves can be dangerous. Inexperienced hikers should never go hiking on glaciers, or enter ice caves without an experienced local guide who is familiar with the area.

Read more: Icelandic hiker who went missing while exploring a Hofsjökull ice cave found dead

Hofsjökull glacier

Hofsjökull glacier The third largest glacier in Iceland. Photo/Vilhelm

The cave is located in Blágnípujökull glacier, an outlet glacier of Hofsjökull. The area is very remote and inaccessible. No roads lead to the cave, which is only accessible by especially equipped mountain trucks and snowmobiles. 

An active volcanic system
The cave where the accident took place was discovered late last year by mountaineers stationed in Kerlingafjöll Highland Center. It was formed by geothermal activity beneath the glacier. Hofsjökull glacier, which rises to an elevation of 1,765 m (5790 ft) and covers 900 sq km (350 sq m) is the third largest glacier in Iceland. The glacier sits on top a major volcanic system. The Hofsjökull volcano, which is hidden beneath the glacier, is believed to be one of the most imposing mountains in the Central Highlands.

Not much is known about possible geothermal or volcanic activity beneath the ice cap, which is 700 m (2300 ft) thick. The volcano, which is not only covered by thick ice, but is also located far from any inhabited areas, is known to have produced a handful of relatively small eruptions since Iceland was settled. Signs of a small glacial outburst flood, most likely caused by melting by geothermal activity, burst from Blágnípujökull glacier in the fall of 2017. The ice cave is believed to have been formed by the same geothermal activity.

A local guide shot the following video inside the cave in early February

After the cave was found several tour companies have organized trips to the cave. Several groups have visited the cave daily in recent weeks. More than a thousand people are estimated to have visited the cave.

Geothermal ice caves are inherently dangerous
The cave extends 150 m (490 ft) beneath the glacier. Unlike ice caves in the glaciers in South Iceland, which are popular tourist destinations, the cave was formed by geothermal activity. There are two types of ice caves: Those formed by meltwater from the glacier and caves formed by geothermal activity. Caves formed by meltwater are far safer than caves formed by geothermal activity. Caves formed by geothermal activity are less stable, which increases the risk of icebergs and chunks of ice falling from the roof or walls of the cave. They also contain poisonous geothermal gases.

Geothermal activity produces high levels of gases, including hydrogen sulfide, H2S. At high concentrations hydrogen sulfide can cause people to fall unconscious. High levels can be fatal. 

High levels of poisonous gases

Blágnípujökull, Kerlingarfjöll
Hofsjökull glacier Blágnípujökull glacier is marked with a red circle. Kerlingafjöll Highland Center is marked with a yellow circle. Photo/

Measurements taken inside the cave in Blágnípujökull on February 17 showed a concentration of 120-183 ppm deep in the cave. Levels above 100 ppm are considered dangerous to life and health. At low levels of concentration H2S can be sensed by smell: It smells like sulfur. But at concentrations above 150 ppm the sense of smell is seriously impaired, which means people can easily be fooled into thinking the level has dropped.

At dangerously high levels hydrogen sulfide can therefore not be detected by smell. Gas detectors are needed at all times inside ice caves created by geothermal activity to monitor the air quality. The group which the man was traveling with had a gas detector, but the man appears to have been separated from the rest of the group.

Not the first accident in the cave

Yesterday's accident was not the first in the cave. In early February a 7 year old girl passed out while visiting the cave with her parents. The child hat sat down on a ledge inside the cave when she suddenly passed out. The girl's mother and travel companions noticed the child passing out. They immediately grabbed the child and ran out of the cave carrying her. The child regained consciousness immediately.

Following this accident the Icelandic Meteorological Office and the Police in South Iceland issued warnings to people to show extreme caution while visiting the cave. 

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