A Geldingadalir window into volcanic processes

 

A screenshot of the volcano from footage provided by RUV.

The volcano in Geldingadalir, Iceland, is still going strong after almost three months since the eruption began. During this time,  it has changed both its form and character. After a few weeks of eruption along multiple vents, the activity is now centred on a single vent, which has grown in size progressively and now dwarfs its neighbouring, extinct ones. Eruption at this vent has varied from the occasionally explosive jets of fragmented lava to relatively quiescent effusion witnessed at present. Last week, Hannah Jane Cohen provided us with a nice, easy-to-understand summary of what the Geldingadalir volcano is telling us about volcanic processes.

Eruption duration

As Cohen notes, the volcano has not met the initial expectations of some of a relatively short-lived eruption. Those expectations were reasonable but probably based as much on gut feeling as scientific evidence. Yes, volcanoes such as the one in Geldingadalir are typically short lived, but how much so is difficult to establish. For extinct volcanoes of this nature, the tools at our disposal do not quite allow us to accurately estimate how long they were active. Further, not too many have erupted during the era of modern volcanological observations, so there are few data on the average or median length of activity. Interestingly, the one well documented example we do have was active for 9 years. The Paricutin cinder cone, with an associated lava flow, is famous for having been born in a Mexican cornfield and was active from 1943-1952. Nine years may well be at the upper end of eruptive durations for this type of volcano but, again, we simply cannot tell for sure. What we can say is that the three-month duration of Geldingadalir volcano does not appear exceptional.  

The Geldingadalir volcano is clearly monogenetic. This means that irrespective of whether it erupts for months or years, it will be active only once in its lifetime. Eruptions may well occur in its vicinity, but magma will find other pathways up to the surface than the one that is feeding this volcano. There are different varieties of monogenetic volcanoes, though, ranging from cinder cones with little associated lava to larger, shield-like forms dominated by thick accumulations of lava, which reflect relatively long-lasting, fairly continuous activity. In fact, these shield volcanoes are common in the ancient volcanological record of Iceland, and they have also been reported from the Snake River Plain in the northwestern United States. They may well be discernable in the ancient, gigantic Deccan Volcanic Province in western India, although nobody has established that with certainty so far. It is possible that the Geldingadalir volcano is developing into a shield, as Icelandic volcanologist Thorvaldur Thordarsson and others have pointed out recently.

The Geldindadalir volcano also offers a view into the Earth's bowels in this part of the world.

Magma source

The Geldindadalir volcano also offers a view into the Earth's bowels in this part of the world. It was apparent early on, based on the lava's make-up and other pieces of evidence, that the volcano was being fed from a great depth, about 17-20 km below the Earth's surface. That takes us to the Earth's mantle, the layer underlying our planet's crust. Because the magma seems to be arriving at the surface directly, without resting in the crust, this volcano can tell us about the nature of the mantle in this region. Notably, some aspects of its composition have changed during the eruption, and such changes could point to a heterogeneous mantle source. That explains part of the excitement of the scientists interviewed by Cohen for her article. 

I was similarly excited in the mid-2000s while conducting doctoral research on (extinct) volcanoes quite like the one in Geldingadalir. The chemical make-up of the volcanic rocks that I sampled also pointed to a mantle source that was compositionally not uniform but instead varied at a smaller scale than was typically considered. I was convinced that those volcanoes in southeastern Oregon would shed light on not only mantle heterogeneity but also the processes of melting, the rates at which the melt was transferred to the surface, the degree to which distinct melts mixed with each other, etc. Unfortunately, I did not have quite the tools to rule out alternative explanations comprehensively and I left academia soon after, so the work remains unpublished. I reproduce a conceptual figure from the dissertation below. Atlhough I have shown a magma chamber in the crust here to encompass all possible cases, there is no evidence that such a chamber exists underneath the Geldingadalir volcano.

Conceptual diagram showing various processes that are likely to be involved in magma generation and evolution with respect to monogenetic volcanoes. From my doctoral dissertation. 

The science of volcanology has only advanced since I was doing my doctoral research. What has not changed, I maintain, is the importance of taking a systems approach to volcanism. The Icelandic and other scientists studying the Geldingadalir eruption are well placed to take such an approach by combining their diverse expertise and state-of-the-art tools. That is all the more reason that I am looking forward to the data coming out of Geldingadalir and their eventual analysis.