Volcanic activity at the seafloor
The greatest number of volcanoes on Earth are hidden from view, occurring in the deep oceans at mid-ocean ridges (where two tectonic plates are spreading apart) or at hot spots (where a mantle plume rises through the oceanic crust). When hot magmas reach the seafloor, the cold seawater rapidly cools the lava and typical structures form such as pillow basalts – lavas that look like actual pillows – and volcanic glass. (See a YouTube video of an underwater eruption).
Interaction between seawater that infiltrates the upper part of the oceanic crust and the high heat coming from the magma source below results in hydrothermal vents, where specifically adapted organisms thrive in the unique chemical conditions of this system. At black smokers, a high-temperature type of vent that emits black clouds of sulfide-rich material, massive sulfide ore deposits of metals such as copper and zinc can be formed.
Researchers from the Centre for Geobiology are studying the volcanic processes and hydrothermal systems that occur on the seafloor of the Arctic ocean on the northernmost parts of the Mid-Atlantic spreading ridge. Compared to other mid-ocean ridges, the two sides of the Arctic ridge are moving apart at very slow rates (less than 20 mm per year) – but hydrothermal systems are nevertheless abundant. In recent cruises, CGB researchers have found hydrothermal vents in the area around the volcanic island of Jan Mayen (#4 on map), as well as the northernmost black smokers at the Loki’s Castle vent field (#7 on map).
Two vent fields were discovered east of the island of Jan Mayen during a research cruise on the G.O. Sars in 2005 (Pedersen et al, 2005). They were named Troll Wall and Soria Moria and occur at water depths of 550 to 700 meters. Hydrothermal activity in the area consists of black smokers emitting high-temperature fluids, as well as abundant iron oxide deposits in the lower temperature areas. Close to these fields, another active venting area was discovered during the 2013 cruise (read here), that will be visited again during this year’s cruise.
Deposits at the Jan Mayen hydrothermal vent field
The small volcanic island of Jan Mayen is situated between Iceland, Greenland and Svalbard. It’s highest peak, the Beerenberg volcano (2277 m), represents the northenmost and only active subaerial volcano in Norwegian territories and erupted last in 1985. The island is formed by the Jan Mayen hotspot.
The island of Jan Mayen and Beerenberg volcano
CGB’s PhD student Eirik Gjerløw spent several months on the island to study its volcanic history. See photos of the island and read Eirik’s reports here.
The world’s northernmost black smokers were discovered at more than 2000 meters water depth during the 2008 cruise, located at the bend between the Mohns ridge and the Knipovich ridge. Unlike most mid-ocean ridges, this section is covered in sediments that are largely derived from the distal part of the Bear Island sedimentary fan. The vent field consists of sulfide mounts with high-temperature fluids venting from black smokers, with low-temperature venting on the slope of these mounts producing barite chimneys. Together with the previous discoveries at Jan Mayen, this find clearly demonstrates that significant venting activity is occurring at ultra-slow spreading ridges.
Temperature measurement at a black smoker at Loki’s Castle