Norway is a country best known for its history, oil, mountains, and an egalitarian attitude to life. Volcanoes are somewhat lacking in this list. But Norway does indeed have one active volcano, given to it by the League of Nations. It is located on the arctic island of Jan Mayen, which became a Norwegian possession, although it is a bit closer to Iceland than to Norway. It is possibly the least studied piece of real estate in Europe.
Jan Mayen is 54 km long and has an area of 380 square km. The climate is cold maritime, and the weather is mostly fog, wind and drizzle. The island consists of two parts. The larger northern part is dominated by the volcano called Beerenberg, 25 km wide and over 2200 meters tall. Beerenberg may be the tallest mountain in the world with a Dutch name! Towards the southwest is a narrow peninsula, 6 km wide and 600 meter high, connected to the northern part by a 2km wide, low isthmus. The inhabited (if not fully habitable) part of the island is the peninsula. The main town is called, somewhat optimistically, Olonkin City, with a population of 15 men and 3 women. People are allowed to live on the island for a maximum of one year.
Jan Mayen may already have been known to the Vikings. Even so, its official discovery was only in 1614. One of the co-discovers was captain Jan May; the island was later named after him. Whaling depleted the natural resources quicker than you can say ‘economic benefit’. The region became economically nonviable within decades and the island was left largely alone until around 1880. There is little flora (Spitsbergen, although much further north, and Greenland are gardens of Eden in comparison), and all terrestrial animals (musk ox, and a dark variety of polar fox) were driven to extinction by Norwegian trappers. Polar bears used to be present but are now only rarely able to reach the island due to the retreating sea ice. The island was declared a nature reserve in 2010, with severe restrictions on (sparse) tourist visits. It is not obvious why it was made a nature reserve – perhaps there are plans to re-establish an eco-system? The reserve protects the volcano, but volcanoes tend not to protect their own environment particularly well!
Whilst all of Jan Mayen has a volcanic origin, the main volcano is the beautiful Beerenberg. It is the northernmost active volcano in the world (discounting any beneath sea level) and the 5th highest volcano in Europe. Beerenberg is covered in impressive glaciers, which until recently reached the sea. They are now retreating and only one calving glacier, Weyprecht, remains. The central crater is 1 km wide, is covered in snow, and is the source of the Weyprecht glacier which flows through a breach in the crater wall.
Beerenberg volcano is in fact fairly active. There were eruptions in 1732, 1818, and possibly 1851, and in the 20th century in September 1970 and January 1985. (Wikipedia and other sites mention an eruption in 1973 but this appears to be incorrect.) Ancient eruptions are recorded in the Greenland ice. Earthquakes occur occasionally, including a magnitude 4.8 earlier this year. Fumarole activity in the crater is common, but the central crater is probably blocked by a cold plug, and all recorded eruptions have been from rifts in the flanks. The mountain is very poorly studied and visits are rare. It is very hard to reach, with the glacier being almost too crevased to be climbable, and the mountain is often invisible due to the perpetual cloud. Some Martian volcanoes may be better known than Beerenberg!
Before the 1970 eruption, the mountain was in fact not considered an active volcano, despite the old reports of eruptions. The 1970 eruption was not noticed even by the people living 30km away but was only discovered days later, from a plane when the eruption column breached the cloud level. The eruption was preceded by earthquakes. It occurred from a 6km long fissure along the eastern side of Beerenberg. The fissure trended northeast, from 600m height at one end to near sea level at the other. There were four main vents along the fissure. It lasted four months, and erupted about 0.5 km3 of lava. On reaching the sea, the flows temporarily added 4 km2 to the island. The lava heated the sea along the island from the usual near-freezing to nearly 30C.
The 1985 eruption occured at the northern tip of the island and was brief, lasting just 40 hours. The older eruptions in 1732 and 1818 occurred at the southern side of Beerenberg. The southern ridge has not erupted for the past 10,000 yr. A 1973 study found indications for three small magma chambers, beneath the south, central, and north parts of the island, consistent with the places of the youngest-looking lava flows and cinder cones.
Jan Mayen’s lavas are basaltic. The north and south are somewhat different: the north has Mg-rich basalts, whilst the south has more evolved basalt such as trachyte, and ryolite. There is a 200-m thick plinian deposit in the south, evidence of past caldera formation. The southern part of the island looks like a late stage of an older volcano. One model sees Jan Mayen Island as migrating volcanism from south to north. At first the volcanism is characterized by mantle derived magma, namely ankaramites. Prolonged activity eventually leads to caldera formation. Post caldera activity is characterized by evolved basalts and trackites. The south has gone through this evolution but the north is still at an early stage.
Jan Mayen is one of the few places where the mid-ocean spreading ridge breaches the surface. Jan Mayen is located near the termination of the Mohns mid-ocean ridge, where it reaches a transform fault called the Jan Mayen Fault Zone. Places where the mid-ocean ridges reach the surface are commonly associated with transform faults.
Jan Mayen Island is the tip of an ice berg. Under water, there is a much larger elevated area, distinct from the spreading ridge. The area extends 300 kilometers towards the south; Jan Mayen island is located near its northern end. To the south it eventually becomes obliterated by the more recent Iceland shelf. This elevated area is called the Jan Mayen microcontinent, Jan Mayen Ridge or Jan Mayen shelf – pick your choice.
The region was at one time located at the heart of the supercontinent Pangea, which formed 300 million years ago. Africa and America started to separate about 175 million years ago, but in the north the crust stretched by some 60 kilometers and subsided, but did not yet break. The subsidence formed a shallow sea, source of the later oil and gas deposits. A brief phase of volcanic activity finally heralded the separation of Greenland and Europe, around 50-55 million years ago, completing the demise of Pangea. There was an extensive but short-lived flood basalt event on Greenland around this time. After the separation, Jan Mayen found itself part of Greenland. The original break-up in this region is often attributed to the Iceland plume popping up underneath an already weakened crust.
The spreading centre at the time was the Aegir Ridge. Aegir spreading slowed down dramatically around 43 million years ago, when a new rift inside Greenland/Jan Mayen developed. The Jan Mayen microcontinent, partly covered by the earlier flood basalts, finally broke off 25 million years ago. Unlike the break-up of Pangea, this break happened without major volcanism: the mantle below the area had grown too cool. The Aegir spreading ridge went extinct, and the currently active (non-volcanic) Kolbeinsey Ridge formed. The microcontinent had jumped plate.
The Jan Mayen shelf rose above water between 30 and 20 million years ago but has been submerged since and is currently 500-1000 meter below sea level. Oil and gas reservoirs are considered likely, due to the close geological relation to the Norwegian continental shelf with its (now heavily depleted) oil deposits. But no exploratory drilling has yet taken place.
The case of the missing hotspot
From Storey et al. 2003, Geology, Volume 32 page 173. ‘EG’ stands for East Greenland. The composition of the Jan Mayen lavas (shown as yellow) are intermediate between Iceland (pink) and Greenland (blue/green) lavas.
Lava fields formed on East Greenland episodically over the next 40 million years, until about 13 million years ago. This was long after the plume had moved away (to Iceland, to be precise): the later volcanism had a different origin. The isotopic compositions of these lavas shows a mix of Icelandic magma and melted ancient crust. The Icelandic magma could date from the Pangea break-up, stored and solidified in the lower crust. The East Greenland lavas come from a later partial melt of this lower crust. The melt could have been caused by new heat from below, or a decrease in pressure from above. The decrease in pressure is considered more likely: it can be caused by erosion, crustal extension, or by the transform fault.
Jan Mayen Island is only 700,000 years old, and is purely volcanic. In the pressure-decrease model, Jan Mayen Island is a consequence of the transform fault; the fact that it is sitting on top of the microcontinent of the same name is accidental but it helped in reaching the surface.
The purported Jan Mayen hotspot remains missing-in-action. Most likely it never existed, but instead it is an imprint of activity of the Iceland hotspot a long time ago. But this is a volcano which guards its secrets well. It may still surprise us.