Earthquakes and the Mid-Atlantic Ridge: Krísuvík in Iceland

Last night allowed me only, I don’t know, three hours of sleep, so my lucidity might be a little off today. I’m also a little giddy after getting my paper on using zircon to unravel the magmatic history of the Okataina Volcanic Complex accepted at Earth and Planetary Science Letters. Nice way to get my week rolling, even if I am a little sleepy.

I’ll try to catch up a bit of the seismicity in Iceland:

A lot of you are following the coverage of the earthquake swarm on Krísuvík, located on the Reykjanes Peninsula, over at Jon Frimann’s blog. He does a good job of summarizing all the seismic activity under the volcano over the last year – it is a busy place. Remember, the whole peninsula is part of the Reykjanes Ridge – a segment of the Mid-Atlantic Ridge system that rises above the ocean surface in Iceland just to the south of Reyjavik. Mid-ocean ridges can be geologically noisy places, earthquake-wise, as there is abundant source magma that can migrate from depth into shallow magma chambers below the ridge. However, it doesn’t necessarily have to be leading to an eruption in the near future. Last year about this time there was another earthquake swarm on the Reykjanes Peninsula that got our attention (of course, a few weeks later another Icelandic volcano made us forget the swarm). Krísuvík has seen over 400 earthquakes over the last 5 days, all tentatively placed between 1-5 km below the surface. You can see all the realtime earthquake data on the Icelandic Meteorological Office website – and looking at the latest data, the swarm has waned some over the past 24 hours since its peak on Friday-Saturday. However, there was also two M4+ earthquakes near Reykjavik over the weekend as well that has gotten the attention of the nation as they were felt in the city (and as the headline of the IceNews article implies, parrots were indeed unhappy.) UPDATE:Jon Frimann is reporting that news services in Iceland (Icelandic) say that the hydrothermal area at Krísuvík has grown since the earthquake swarm began. Changes in hydrothermal systems are common in magmatically active areas – in fact, changes in the amount of hydrothermal circulation can generate earthquakes on their own … but seems like more to watch at Krísuvík.

As I mentioned above, Krísuvík is part of the Mid-Atlantic Ridge that comes above sea level on the Reykjanes Peninsula in southwestern Iceland. The volcano itself likely last erupted in 1340 A.D. As with all of the volcanoes along the Peninsula, the eruption was a fissure vent that produced basaltic lava flows and minor explosions (all VEI ~1) – Hawaiian-style volcanism. Any explosive behavior is likely the result of interactions of the basalt with the active hydrothermal circulation on the Peninsula. Krísuvík had more eruptions in 1151-1188, all in the VEI 1 fissure vent style. However, prior to the arrival of the Norse in Iceland, there are some deposits that suggest some larger eruptions (VEI 2) over the last few thousand years. Krísuvík does have abundant hydrothermal activity as well, in the form of hot springs and mudpots and the volcano saw as much as 3 cm of uplift in 2009. Other parts of the Reykjanes Peninsula have erupted more recently – with the namesake volcano for the peninsula erupting in 1926.

Top left: Hydrothermal field on Krísuvík in Iceland as seen in September 2008.