̽��ֱ�� of Cambridge - John Maclennan

Lava from 2021 Icelandic eruption gives rare view of deep churnings beneath volcano

cmm201 — Fri, 16 Sep 2022 14:30:00 +0000

̽��ֱ��study, published in the journal Nature and led by the ̽��ֱ�� of Iceland, reports that the eruption was unusual because it was supplied by a particularly deep reservoir of magma originating around 15 kilometres beneath the surface, at the base of Earth’s crust.

Their results also show that volcanoes like this can be fed by complex plumbing systems, where different batches of magma can mix and travel to the surface in just a matter of days or weeks.

̽��ֱ��researchers took measurements of lava and volcanic gases during the first 50 days of the eruption — giving them a near-real time report on the changing magma supply.

“I never expected to see the chemical composition of erupting lava change this quickly, showing us just how fast things can change in the depths beneath volcanoes,” said Simon Matthews from the ̽��ֱ�� of Iceland.

̽��ֱ��chemical fingerprint of lavas and the crystals inside them — together with the volcanic gases erupted — helped the researchers decode where the magma originated from and its journey to the surface. Until now, there has been a lack of information about the deepest parts of magmatic systems.

̽��ֱ��results showed that, during the initial phases of the eruption, the lava was predominately coming from around the boundary between the crust and underlying mantle – the thick, rocky layer that makes up most of Earth’s interior. But over the following weeks, the composition of the lava changed, indicating the eruption was directly tapping magma from greater depths.

“Ever since Enlightenment thinkers started writing about volcanoes, scientists have drawn cross-sections to visualise how they might work below ground,” said co-author Professor Clive Oppenheimer from Cambridge’s Department of Geography. “This study draws together different strands of information from monitoring the chemistry of lava and gas emissions to describe what is happening up to 20 kilometres down.”

They used indicators including the magnesium contents of the lava and carbon dioxide levels in the volcanic gases as barometers to gauge how hot and deep the magma feeding the eruption was. They suggest that, for the magma to come from 15 kilometres below the surface, the eruption was fed by something like a high-speed train direct to the mantle.

“We’ve known for a while that magma coming from the mantle is variable,” said co-author Professor John Maclennan from Cambridge’s Department of Earth Sciences, “But we’ve had to work hard to find clues as to how this complex mixing happens.”

̽��ֱ��authors point out that it has long been argued that different kinds of magma can mix deep in magmatic systems before an eruption. ̽��ֱ��new research shows that new magma can flow into a deep reservoir and mix with existing magma rapidly, in as little as 20 days.

Normally scientists use lavas erupted from old or extinct volcanoes to get a below ground view of volcanoes. But these samples are often too old to unravel processes happening over the course of a few days, “I’ve looked at hundreds of samples from dead volcanoes, but never had the chance to observe such a spectacular example of magma mixing in real-time,” said Maclennan.

Magma mixing has been shown to be an important process in triggering volcanic eruptions, so the study findings could have implications for understanding what drove the eruption and for future monitoring of volcanic activity in Iceland and at similar volcanoes.

Reference:
Sæmundur A. Halldórsson et al. ‘Rapid shifting of a deep magmatic source at Fagradalsfjall volcano, Iceland.’ Nature (2022). DOI: 10.1038/s41586-022-04981-x.

After centuries without volcanic activity, Iceland’s Reykjanes peninsula sprang to life in 2021 when lava erupted from the Fagradalsfjall volcano. New research involving the ̽��ֱ�� of Cambridge helps us see what is going on deep beneath the volcano by reading the chemistry of lavas and volcanic gases almost as they were erupted.

I’ve looked at hundreds of samples from dead volcanoes, but never had the chance to observe such a spectacular example of magma mixing in real-time

John Maclennan

Fagradalsfjall volcano

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‘Crystal clocks’ used to time magma storage before volcanic eruptions

sc604 — Thu, 18 Jul 2019 18:00:00 +0000

Researchers from the ̽��ֱ�� of Cambridge used volcanic minerals known as ‘crystal clocks’ to calculate how long magma can be stored in the deepest parts of volcanic systems. This is the first estimate of magma storage times near the boundary of the Earth’s crust and the mantle, called the Moho. ̽��ֱ��results are reported in the journal Science.

“This is like geological detective work,” said Dr Euan Mutch from Cambridge’s Department of Earth Sciences, and the paper’s first author. “By studying what we see in the rocks to reconstruct what the eruption was like, we can also know what kind of conditions the magma is stored in, but it’s difficult to understand what’s happening in the deeper parts of volcanic systems.”

“Determining how long magma can be stored in the Earth’s crust can help improve models of the processes that trigger volcanic eruptions,” said co-author Dr John Maclennan, also from the Department of Earth Sciences. “ ̽��ֱ��speed of magma rise and storage is tightly linked to the transfer of heat and chemicals in the crust of volcanic regions, which is important for geothermal power and the release of volcanic gases to the atmosphere.”

̽��ֱ��researchers studied the Borgarhraun eruption of the Theistareykir volcano in northern Iceland, which occurred roughly 10,000 years ago, and was fed directly from the Moho. This boundary area plays an important role in the processing of melts as they travel from their source regions in the mantle towards the Earth’s surface. To calculate how long the magma was stored at this boundary area, the researchers used a volcanic mineral known as spinel like a tiny stopwatch or crystal clock.

Using the crystal clock method, the researchers were able to model how the composition of the spinel crystals changed over time while the magma was being stored. Specifically, they looked at the rates of diffusion of aluminium and chromium within the crystals and how these elements are ‘zoned’.

“Diffusion of elements works to get the crystal into chemical equilibrium with its surroundings,” said Maclennan. “If we know how fast they diffuse we can figure out how long the minerals were stored in the magma.”

̽��ֱ��researchers looked at how aluminium and chromium were zoned in the crystals and realised that this pattern was telling them something exciting and new about magma storage time. ̽��ֱ��diffusion rates were estimated using the results of previous lab experiments. ̽��ֱ��researchers then used a new method, combining finite element modelling and Bayesian nested sampling to estimate the storage timescales.

“We now have really good estimates in terms of where the magma comes from in terms of depth,” said Mutch. “No one’s ever gotten this kind of timescale information from the deeper crust.”

Calculating the magma storage time also helped the researchers determine how magma can be transferred to the surface. Instead of the classical model of a volcano with a large magma chamber beneath, the researchers say that instead, it’s more like a volcanic ‘plumbing system’ extending through the crust with lots of small ‘spouts’ where magma can be quickly transferred to the surface.

A second paper by the same team, recently published in Nature Geoscience, found that that there is a link between the rate of ascent of the magma and the release of CO2, which has implications for volcano monitoring.

̽��ֱ��researchers observed that enough CO2 was transferred from the magma into gas over the days before eruption to indicate that CO2 monitoring could be a useful way of spotting the precursors to eruptions in Iceland. Based on the same set of crystals from Borgarhraun, the researchers found that magma can rise from a chamber 20 kilometres deep to the surface in as little as four days.

̽��ֱ��research was supported by the Natural Environment Research Council (NERC).

References:
Euan J.F. Mutch et al. ‘Millennial storage of near-Moho magma.’ Science (2019). DOI: 10.1126/science.aax4092

Euan J.F. Mutch et al. ‘Rapid transcrustal magma movement under Iceland.’ Nature Geoscience (2019). DOI: 10.1038/s41561-019-0376-9

̽��ֱ��molten rock that feeds volcanoes can be stored in the Earth’s crust for as long as a thousand years, a result which may help with volcanic hazard management and better forecasting of when eruptions might occur.

This is like geological detective work

Euan Mutch

Bob White

Magma erupting at the Holuhraun lava field in August 2014

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