Spectacular images of recent volcanic eruptions in Hawaii are a little disheartening – especially given news reports suggesting there is a sleeping volcano under Melbourne that could awaken and erupt at any moment.

Understanding the geological differences between Melbourne and Hawaii is really helpful in working out how we can keep an eye on future risks in Australia.

The Newer Volcanics Province

Victoria and South Australia do host an active volcanic field, called the Newer Volcanics Province (NVP). This is not a single volcano with a large single chamber of molten rock (magma) — the common image of a volcano — but a widespread field of multiple small volcanoes, each with a small volume of magma.

Melbourne lies at the eastern end of the NVP, and the most recent eruptions in this area occurred over a million years ago.

Mt Gambier in southeastern South Australia represents the western margin of the volcanic field and the most recent eruption — only 5,000 years ago.

Between Melbourne and Mt Gambier there are more than 400 small volcanoes that erupted over a period of 6 million years.

The NVP was most active between 4.5 million to 5,000 years ago and volcanologists consider the field to still be “active” with the potential for future eruptions.

We do not know when the next eruption will take place.

Volcanoes of the Newer Volcanics Province (a) Mt Napier, SE of Hamilton (b) The Noorat complex (c) The Mt Gambier Volcanic Complex, near Mt Gambier (d) The Mt Schank Volcanic Complex, near Mt Gambier (e) Purrumbete volcano, near Camperdown (f ) Tower Hill volcano, near Warrnambool (g) The Red Rock Volcanic Complex, near Colac.
Ray Cas and co authors

The NVP is located within a tectonic plate – and not along a plate edge like the Ring of Fire volcanoes (for example, Mt Agung on Bali).

Tectonic plates are large slabs of rock made up of the Earth’s crust and uppermost part of the mantle (the lithosphere) which form the outer shell of the Earth, and move around slowly relative to each other.

Volcanoes act in different ways

While Kilauea volcano in Hawaii is also located within a tectonic plate, it has several key differences with the NVP in Southeastern Australia.

Magma source and volume

While Hawaii sources large volumes of magma from deep within the Earth, the NVP only receives small amounts of magma from just below the Earth’s crust.

It’s worth noting here that the makeup of the magma is similar in both locations, with both erupting runny basalt – a type of rock low in silica, and high in iron and magnesium.

We suspect that in Australia’s NVP, magma can move very fast from its source to the surface (on a time scale of days). This can bring rock fragments of the mantle (xenoliths) to the surface as the magma moves too fast for them to melt.

Fragments of the mantle (xenoliths) in a volcanic bomb erupted at Mt Noorat, brought to the surface by ascending magma.
Ray Cas

Eruption frequency

Hawaiian volcanoes can erupt numerous times, but NVP volcanoes are largely monogenetic — that is, each only erupt once or over a restricted period of time.

Crust thickness

Hawaii is located on the oceanic crust of the Pacific Tectonic Plate, which is a thin (around 7 km) layer of material that is dense and rich in iron. The magma can rise through this crust quite easily.

In contrast, the NVP is located on continental crust which is much thicker (about 30km), richer in silica and much less dense. Magma finds it much harder to travel through this kind of material.

Water adds danger

The explosivity of a volcanic eruption can depend on availability of water.

“Dry” eruptions – where magma has little-to-no interaction with ground water or water on the Earth’s surface – typically produces mildly explosive eruptions such as lava fire fountains, showers of lava fragments and lava flows.

The most explosive, hazardous eruptions form where rising magma interacts with ground water, surface water or sea water. These “wet”, (phreatomagmatic) eruptions can produce deadly, fast moving, ground-hugging currents of gas and volcanic material – called pyroclastic surges, and send abundant fine volcanic ash into the atmosphere.

The Australian Mt Gambier eruption 5,000 years ago was a “wet” eruption, and had a volcanic explosivity index of 4 on a scale of 0-8 (where 0 represents a lava eruption, 1 a spectacular lava “fire” fountain as recently witnessed in Hawaii, and 8 represents a catastrophic explosive super-eruption).

The accompanying ash column is estimated to have reached 5km to 10km into the atmosphere.

On Hawaii explosive eruptions are rarer because the magma has a low gas content and groundwater aquifers are not as large as in the NVP. However, when lava flows into the sea there are often phreatic or steam explosions which can be hazardous to nearby spectators.

Mt Gambier’s Blue Lake was created by a huge volcanic eruption.
from www.shutterstock.com

There’s a lot we don’t know

Another important factor relates to how we keep an eye on volcano risk at the two sites. Kilauea on Hawaii is extremely well monitored, and tracking magma moving underground has helped predict eruptions.

In contrast, the NVP is less well monitored, likely because there is no present volcanic activity, and it’s a huge region.

However, warning signs of an eruption are likely to be similar in the NVP to those on Hawaii – small earthquakes, minor uplift and/or subsidence of the ground, changes in ground temperature and gas or steam rising out of the ground.

Also, based on present knowledge of the NVP, there is no clear eruption pattern we can use to try to predict when or where the next eruption will be.

If the NVP were to erupt, significant impacts on our lives would likely occur. These may include:

the closure of surrounding roads by lava flows and ash fallout
volcanic ash and rocks loading roofs of local buildings
contamination of water reservoirs by ash
damage to machinery and electricity infrastructure by infiltrating ash
respiratory problems for people prone to asthma, and
disruption to air traffic across southeastern Australia due to drifting ash clouds driven by prevailing south-westerly winds.

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Further scientific research is required on active volcanic fields such as the NVP to know how fast magma travels from its source to the surface, how much warning we might have before an eruption, and how long an eruption and its impacts might last.

Heather Handley, Associate Professor in Volcanology and Geochemistry, Macquarie University; Jozua van Otterloo, Assistant Lecturer in Volcanology, Monash University, and Ray Cas, Professor emeritus, Monash University

This article was originally published on The Conversation. Read the original article.

Maui

Hawaii: Big Island

Lava in Hawai’i is reaching the ocean, creating new land but also corrosive acid mist

Dave McGarvie, The Open University and Ian Skilling, The University of South Wales

There is something special and awe-inspiring about watching new land form. This is what is now happening in Hawai’i as its Kīlauea volcano erupts. Lava is reaching the ocean and building land while producing spectacular plumes of steam. These eruptions are hugely important for the creation of new land. But they are also dangerous. Where the lava meets the ocean, corrosive acid mist is produced and glass particles are shattered and flung into the air. Volcanic explosions can also hurl lava blocks hundreds of metres and produce waves of scalding hot water.

At Kīlauea, lava is erupting from a line of vents on the volcano’s flanks, and is moving downslope to the edge of the island, where it enters the ocean. This is a process that has been witnessed many times at Hawai’i and other volcanic islands. And it is through many thousands of such eruptions that volcanic islands like Hawai’i form.

The new lava being added to Hawai’i by this latest Kīlauea eruption replaces older land that is being lost by erosion, and so prolongs the island’s lifespan. In contrast, older islands to the north-west have no active volcanoes, so they are being eroded by the ocean and will eventually disappear beneath the waves. The opposite is happening to the south-east of Hawai’i, where an underwater volcano (Lōʻihi Seamount) is building the foundations of what will eventually become the next volcanic island in this area.

How lava gets to the ocean at Hawai’i

The lava erupting from the current Kīlauea vents has a temperature of roughly 1150 degrees °C, and has a journey of between 4.5km and 5.5km to reach the ocean. As this lava moves swiftly in channels, it loses little heat and so it can enter the ocean at a temperature of over 1000 degrees°C.

When lava meets the sea, new land is formed.
EPA

What happens when lava meets the ocean?

We are witnessing one of the most spectacular sights in nature – billowing white plumes of steam (technically water droplets) as hot lava boils seawater. Although these billowing steam clouds appear harmless, they are dangerous because they contain small glass shards (fragmented lava) and acid mist (from seawater). This acid mist known as “laze” (lava haze) can be hot and corrosive. If anyone goes to near it, they can experience breathing difficulties and irritation of their eyes and skin.

Apart from the laze, the entry of lava into the ocean is usually a gentle process, and when steam is free to expand and move away, there are no violent steam-driven explosions.

But a hidden danger lurks beneath the ocean. The lava entering the sea breaks up into blobs (known as pillows), angular blocks, and smaller fragments of glass that form a steep slope beneath the water. This is called a lava delta.

A newly formed lava delta is an unstable beast, and it can collapse without warning. This can trap water within the hot rock, leading to violent steam-driven explosions that can hurl metre-sized blocks up to 250 metres. Explosions occur because when the water turns to steam it suddenly expands to around 1,700 times its original volume. Waves of scalding water can also injure people who are too close. People have died and been seriously injured during lava delta collapses

So, the ocean entry points where lava and seawater meet are doubly dangerous, and anyone in the area should pay careful attention to official advice on staying away from them.

Pillow Lavas form underneath the ocean.
National Oceanic & Atmospheric Adminstration (NOAA)

What more can we learn from these eruptions?

Once lava deltas have cooled and become stable they represent new land. Studies have revealed that lava deltas have distinctive features, and this has enabled volcanologists to recognise lava deltas in older rocks.

Remarkable examples of lava deltas have been discovered near the top of extinct volcanoes (called tuyas) in Iceland and Antarctica. These deltas can only form in water and the only plausible source of this water in this case is melted ice. This means that these volcanoes had melted water-filled holes up to 1.5km deep in ice sheets, which is an astonishing feat. In fact, these lava deltas are the only remaining evidence of long-vanished ice sheets.

It is a privilege to see these incredible scenes of lava meeting the ocean. The ongoing eruptions form part of the natural process that enables beautiful volcano islands like Hawai’i to exist. But the creation of new land here can also bring danger to those who get too close, whether it be collapsing lava deltas or acid mist.

Dave McGarvie, School of Physical Sciences, The Open University and Ian Skilling, Senior Lecturer (Volcanology), The University of South Wales

This article was originally published on The Conversation. Read the original article.

Eruptions and lava flows on Kilauea: but what’s going on beneath Hawai’i’s volcano?

Chris Firth, Macquarie University

Over the past few weeks we’ve seen increasingly spectacular images reported in the news of the ongoing eruption at Kilauea volcano, on the Pacific island of Hawai’i.

These have been tempered by reports of growing destruction, with houses and infrastructure bulldozed, buried or burned by lava flows.

Yet Kilauea is one of the world’s most active volcanoes, and has been erupting continually since 1983. So what has triggered this sudden change in activity, threatening homes and livelihoods? The answer relates to what is happening beneath the volcano.

Kilauea volcano

Activity at Kilauea is driven by the buoyant upwelling of a plume of hot mantle, which provides the heat to generate magma beneath the volcano. This magma has the potential to erupt from several different locations, or vents, on the volcano.

Click on the three blue markers to reveal more.
Google Maps/The Conversation

Typically, the crater at the summit of the volcano is where eruptions are expected to occur, but the geology of Kilauea is complex and a rift on the eastern side of the volcano also allows magma to erupt from its flanks.

Over the past decade both the summit crater and a vent on the eastern rift, called Pu’u O’o, have been continually active. The summit crater has hosted a lava lake since March 2008.

Lava lakes are relatively rare features seen at only a handful of volcanoes around the world. The fact that they do not cool and solidify tells us that lava lakes are regularly replenished by fresh magma from below.

In contrast, Pu’u O’o, 18km east of the summit crater, has been pouring out lava flows since 1983. In the first 20 years of this eruption, 2.1km³ of lava flows were produced, equivalent in volume to 840,000 Olympic swimming pools. All of this tells us that Kilauea volcano regularly receives lots of magma to erupt.

Current eruptions

Over the past three weeks activity at Pu’u O’o has stopped, while a series of fissures has opened roughly 20km further east in a subdivision known as Leilani Estates.

This area was previously affected by lava flows in 1955.

To date, 23 fissures have opened, starting off simply as cracks in the ground, with some developing into highly active vents from which significant lava flows are forming.

At the moment, the longest flows are about 6km long, having reached the ocean. This is a further cause for concern, as the lava reacts with seawater to form a corrosive mist.

Meanwhile, at the summit of the volcano, the lava lake has drained from the crater, sparking fears of more explosive eruptions, as draining magma interacts with groundwater.

Satellite instruments and high-resolution GPS are being used to monitor changes in the shape of the volcano and have found that the summit region is deflating, while the lower east rift zone, where new fissures have opened in recent days, is inflating.

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The magma reservoirs that feed eruptions on Kilauea can be imagined as balloons, which grow when they are filled and shrink when they are emptied. Deflation at the summit, combined with observations that the lava lake has drained (at a rate of up to 100m over two days!), suggest that the magma reservoir feeding the summit is emptying.

Where is the magma going? Observations of ground inflation around the newly opened fissures to the east indicate that the magma is being diverted down the east rift and accumulating and erupting there instead.

Exactly what has caused this rerouting of the magma is still not clear. A magnitude 6.9 earthquake occurred in the area on May 4 and this may have opened a new pathway for magma to erupt, influencing the geometry of the lower east rift zone.

A Landsat8 image (top) of Kilauea volcano taken on March 15, 2018. The relative location of the various vents are marked, and a red, glowing lava flow can just be seen in the north-east of the image. The graphic (bottom) shows an inferred magma pathway below the volcano.
NASA/Chris Firth, Author provided

Lessons for the future

By combining measurements from Kilauea of ground deformation, earthquake patterns and gas emissions during the current eruption, with observations of the lava that is erupted, volcanologists will be able to piece together a much clearer picture of what triggered this significant change in eruption over the past few weeks.

This knowledge will be crucial in planning for future eruptions, both at Kilauea and at other volcanoes.

Eruptions from the flanks of a volcano can pose a much more significant hazard for the local population than those from a volcano’s summit, as many more people live in the areas that are directly affected.

This has been amply displayed over the past few weeks on Kilauea by the fissures opening in people’s gardens and lava flows destroying homes and infrastructure.

But Kilauea is not the only volcano to have flank eruptions. For example, lava flows famously emerged from the lower slopes of Mt Etna in 1669, destroying villages and partially surrounding the regional centre of Catania, on the east coast of Sicily, Italy.

Lessons learned from the current eruption of Kilauea can equally be applied to other volcanoes, like Etna, where more densely populated surroundings mean that the hazards posed by such an eruption would be even greater.

Lava fountains form fissure 22 on the lower east rift zone of Kīlauea volcano, in Hawai’i.
USGS

Chris Firth, Lecturer in Geology, Macquarie University

This article was originally published on The Conversation. Read the original article.

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