The mysterious rumbling noises heard emanating from the tuya Herðubreið have a very mundane explanation.
Harpa Grímsdóttir of the Icelandic Met Office told Vísir that according to their findings, the source of the rumbling heard earlier this week was a landslide. Specifically, melting snow gave way along the northeast slope, taking with it a layer of rocks and debris.
Harpa advises that people tread carefully around the bottom of some of the sheerer faces of the volcano, as there is still an unusual amount of snow along the eastern slope.
As reported, Icelandic rescuers who had been searching for a group of French tourists found them on Wednesday at the foot of Herðubreið safe and sound, although they said there had been an avalanche. News of the avalanche was reported, but upon further inspection, no evidence of an avalanche could be found – except for the rumbling.
This prompted further inspection of the area, which revealed that a landslide caused by an avalanche was the culprit. Part of the reason why this cause may have gone unnoticed initially is because avalanches and landslides are very rare during summer months.