Geology of Reykjanes Peninsula
After the eruption of the Fagradalsfjall volcano on 19 March 2021, National Geographic's experts predicted that this "may mark the start of decades of volcanic activity".
At this time, the Snæfellsnes-Skagi rift had drifted so far to the west and away from the presumed steady place hot spot, that activity shifted eastwards in direction of this mantle plume which is now thought to be situated under the big glacier shield of Vatnajökull.
[4] The topography of Reykjanes Peninsula was formed by glaciers and volcanism, basaltic lava fields covering a good part of the peninsula, in between volcanoes of subglacial as well as subaerial origin, namely tuyas, hyaloclastic ridges (tindars), shield volcanoes and crater rows.
Both volcanoes partially formed Esja and the smaller mountains near Reykjavík and the hills on the islands and small peninsulas like Viðey and Kjarlarnes.
[1] The Holocene shield volcanoes represent the great bulk of magma production in this part of Iceland and form the base of many other volcanic landforms.
[10] Sandfellshæð is a very regularly constructed shield volcano and the largest in the southern part of Reykjanes Peninsula.
Since the end of the Pleistocene glaciation (15,000–11,000 years ago in the region),[1] Holocene volcanoes have contributed to the basaltic lava fields of the peninsula.
[14][15] One of the reasons for the varying number of systems in the literature is that geothermal areas, magnetic anomalies, eruptive centers, and geochemistry do not all align.
[16] Only the Hengill volcanic system, the most eastern system, has an additional central volcano and this volcano is complex as it is at the intersection with the West volcanic zone of Iceland and South Iceland seismic zone,[17][18] forming the Hengill triple junction.
[13]: 17512 Otherwise, the volcanic systems, because they are on top of a rift segment, show a tendency for basaltic fissure eruptions.
[21] These earthquakes often take place within the volcanic systems, but there are also many faults, fractures and fissures in the N-S direction on the peninsula.
The larger earthquakes are felt and registered on Reykjanes Peninsula, and they can also trigger medium-sized quakes in this region, as last seen in 2008 and especially in 2000.
[14] The spreading that occurs generates NE-SE trending fissure swarm faulting and connects the area with the other surrounding rift zones.
The first, from 950 to 1240, culminated in the lengthy series of eruptions between 1210 and 1240 called the Reykjanes Fires that deposited substantial amounts of lava and tephra across the peninsula.
[31] The eruption was small and effusive, from a 500–800 m long fissure; National Geographic predicted that this volcano was unlikely to threaten "any population centers".
[32] On 10 July 2023 at 16:40 UTC, a fissure eruption began adjacent to the summit of Litli-Hrútur and ended by the beginning of August 2023.
Beginning in late October 2023, an intense series of earthquakes in and around Grindavík prompted the evacuation of the town, as a large underground magmatic intrusion indicated that an eruption in the area was imminent.
[35] Further brief effusive eruptions with a very rapid outflow of large quantities of lava took place on 14 January and 8 February 2024, damaging the outskirts of Grindavik and other infrastructure in the area.
