Wednesday, September 28, 2022

There she blows: the internal ‘magma filter’ that drives ocean island volcanoes to erupt

The volcanoes we see on Earth’s surface are just the tip of an iceberg. Below the surface, they are fed by an intricate network of conduits and reservoirs that bring molten rock to the surface, called magma.

When magma erupts, it can generate lava flows that cool and become volcanic rock. These rocks hold important clues about the inner workings of volcanoes, and what caused them to erupt in the past. But decoding these clues is a trickier task.

Our new research, published in the journal Geology, reveals previously hidden information in the chemistry of erupted lava. Interestingly, we found that many volcanoes have an internal “filter” that prompts them to erupt.

If we can detect magma at this critical tipping point inside a volcano, it could also help us gauge when an eruption is imminent.

Hotspot Volcano

Most volcanoes, such as those in the Pacific Ring of Fire and the Mid-Atlantic, are on the boundaries between tectonic plates. But some volcanoes, including those that make up the Hawaiian Islands, occur where hot plumes from inside the Earth reach the surface. These are known as “hotspot” volcanoes.

Australia hosts the longest track of hotspot volcanoes in a continental setting. Over tens of millions of years, volcanoes such as The Glass House Mountains in Queensland, or Wollumbin (Mount Warning) in New South Wales tracked the movement of the Australian continent over a stable hotspot.

In the oceans, hotspots form a chain of paradise islands such as Hawaii, the Galapagos or the Canary Islands. These oceanic island volcanoes were previously thought to have formed from magma tens of kilometers below the surface, deep in the Earth’s mantle.

But our new research suggests that ocean islands may be erupting volcanic magma that has been filtered and modified at shallow depths.

crystal-rich, not crystal clear

Volcanic lava often consists of crystals from inside the volcano, mixed with erupted magma. Crystals tell us a lot about the interior of a volcano, but they can also hide the chemistry of lava.

Read more: Volcanic crystals could make it easier to predict eruptions

Think of it like Rocky Road chocolate. If we want to analyze the ingredients of chocolate itself, we first have to disregard marshmallows and nuts.

Microscopic image of crystals in magma.
author provided

We can do this by analyzing rocks made of crystal-free lava. In our study, we compared crystal-free and crystal-rich magma from the El Hierro volcano in the Canary Islands, which last erupted in 2011.

It turns out that the crystal-free magma from these volcanoes has millions of years of volcanic activity and is similar in many oceanic island volcanoes around the world, including the Canary Islands and Hawaii. This is how we realized that the magma was not pristine and was coming directly from great depths, but was filtered at shallow depths.

And if the magma from hotspot island volcanoes is similar, it is likely that their eruptions are triggered by a normal mechanism as well.

‘Secret Volcano Filter’

When crystals form inside a volcano, it “steals” chemical elements from the magma. In turn, this changes the composition of the remaining magma, almost as if it were passed through a sieve.

This filtering process makes magma less dense, and increases its gas content. This gas can then bubble up and carry magma to the surface, just like a cork coming out of a champagne bottle.

In ocean island volcanoes, magma can reach this “tipping point” at the base of the Earth’s crust, which is a few kilometers below the surface rather than at depth. This means that if we detect magma at this depth with the help of earthquake monitoring equipment, an eruption can occur. That’s exactly what happened during the 2011 El Hierro eruption.

el hierro undersea explosion
Undersea volcanic activity during the 2011 eruption of El Hierro.
Spanish Civil Guard/AAP

Does this make it easier to predict eruptions?

If we could open a volcano like a doll’s house, we would be able to track the movement of magma towards the surface. It’s a pity that we can’t, although we can try to “see” this journey indirectly by monitoring earthquakes, deformation and gas emissions, all of which may indicate magma rising inside the volcano Huh.

But to assess whether a volcano is likely to erupt, or whether a dormant volcano is resurfacing, we also need to compare current observations with information about eruptions in the past.

This is where our new discovery may prove particularly useful. If eruptions are triggered at similar depths in ocean island volcanoes globally, warning signals from such depths may be particularly important to monitor and consider as precursor signals to eruptions.

Read more: Australia’s volcanic history is much more recent than you might think

This article is republished from – The Conversation – Read the – original article.

Nation World News Desk
Nation World News Desk
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