⚡Iceland Explorer's video: Helgafell Explosive Subglacial Eruption in Reykjavik Area Krysuv k Volcanic System Iceland

Helgafell (Holy Mountain) is volcanic mountain in Hafrnarfjordur (Reykjavik Capital Area). 4K Drone. Filmed on October 9th, 2021. The mountain is situated within the area of the Krýsuvík volcanic system. It “is thought to have formed in a single subglacial fissure eruption under at least 500 m of glacial ice“. The original ridge was about 2km long. Some Holocene lava flows, also from the neighbouring Brennisteinsfjöll volcanic system, surrounded the mountain later. Helgafell is made mostly from palagonite, i.e. palagonitized tephra, dikes and a small amount of pillow lava. Helgafell is most probably a monogenetic subglacial mound, because no traces of subaerial eruptions were found on its slopes. The ice sheet under which the Helgafell eruptions took place, was about 500 m thick at time of eruption. In the beginning a fissure opened at right angles to the ice flow, which was from the southeast to the northwest. It was about 15 km from the glacier snout. There is a big terminal moraine at the coast at Álftanes. Rapid ice melting was the consequence of explosive eruption and therefore magma fragmentation from the start of the eruption. At Helgafell next an edifice was formed about 300 m high in an ice vault, meltwater drained away very fast through subglacial channels so that the explosive activity continued to the end, which seems to have been after some days. This explains the fact, that Helgafell is next to overall made from mafic hyaloclastite, whereas most other researched smaller subglacial volcanoes showed a basis of pillow lavas. Of these and some small intrusions, the researchers just found minimal quantities. Wind erosion removed part of the summit in the Holocene and other parts of the mountain slumped. The lava fields surrounding Helgafell today are about 40–80 m in thickness as gravity surveys showed. Dont confuse Helgafell in Hafnarfjordur with Helgafell in Vestmannaeyjar Islands, I have a video about Eldfell and the "Other Helgafell" too - https://www.youtube.com/watch?v=kO_IOIcHvSk&t=395s