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.

The ConversationIt 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.

From Kilauea to Fuego: three things you should know about volcano risk


Heather Handley, Macquarie University

Recent photographs and video from the devastating eruption of Fuego volcano in Guatemala show people stood watching and filming hot, cloud-like flows of gas, ash and volcanic material (known as pyroclastic flows) travelling towards them down the slopes of the volcano.

From this it is clear that some people do not fully understand the risks of the volcanoes they live near.

Although each volcano is different, and each presents different risks to the people near to them, there are some generalisations that help us understand what these risks are likely to be.

Three points are clear: location matters, explosiveness can be predicted to an extent, and fast-moving pyroclastic flows of volcanic material are deadly.




Read more:
Fuego volcano: the deadly pyroclastic flows that have killed dozens in Guatemala


1. Location matters

The outer layer of the Earth, called the lithosphere (crust and upper mantle), is broken up into a number of rigid tectonic plates. Volcanoes typically occur where the plates move apart from one another, for example at underwater mid-ocean ridges, or collide together at subduction zones.

Australia sits in the middle of a tectonic plate – whereas New Zealand sits on a boundary between two tectonic plates. CLICK ON IMAGE TO ZOOM
from www.shutterstock.com

We also find volcanoes in the middle of tectonic plates – these are called “intraplate” volcanoes, such as the Hawaiian and Galápagos oceanic islands.

The magma (molten rock) that feeds volcanoes is generated in different ways in these settings, and different volcanic landforms result.

Hawaii is in the middle of a tectonic plate and volcanic activity there forms relatively low-profile, shield volcanoes. Typically, these volcanoes are built up by many fluid lava flows into broad, gently sloping domes, which resemble a warrior’s shield.

In contrast, Fuego is situated in a subduction zone environment (one plate going under another) where steep-sided, stratovolcanoes, or composite volcanoes are most common. These often symmetrical, conical volcanoes form from the build up of layers of lava and pyroclastic (fragmented volcanic) rocks.

2. Magma and gas affect explosiveness

The volcanic landforms and eruptive styles we see in different settings are largely a result of the differences in the composition of the magma (molten rock) erupted, its temperature and its gas content in these contrasting tectonic settings.

Large shield volcanoes in the middle of tectonic plates, such as Kilauea volcano in Hawaii, erupts high temperature, low silica lava. This is runnier (less viscous) than magma typically erupted at subduction zone volcanoes (like Fuego).




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


This means that any volatiles (dissolved gases such as water, carbon dioxide and sulphur dioxide) in the Kilauea magma are able to escape more easily compared to in a stickier, higher silica, magma that characterises subduction zone volcanoes.

And so “Hawaiian-style” eruptions are characterised by lava fountaining and flows of hot fluid lava that normally travel slow enough for people to walk away from and evacuate. This is exactly what we have been seeing over the last month in Kilauea’s East Rift Zone.

In contrast, at subduction zone volcanoes – such as Fuego – the higher water content of the magma and the typically more silica-rich, sticky magmas erupt more explosively. It is harder for gas bubbles formed to escape as magma rises to the surface, which then take up more space and over pressure the system.

Subduction zone volcanoes can produce high columns of gas and ash reaching tens of kilometres into the atmosphere, and scalding hot, fast-moving, cloud-like currents of gas, ash and volcanic material. These pyroclastic flows, or “pyroclastic density currents”, race down the volcano at speeds over 80 km/hr.

Some news reports of eruptions at Fuego have incorrectly termed these pyroclastic flows “rivers of lava”. They are very different to lava flows and much more hazardous.

Clear and accurate communication of volcanic eruptions is crucial if those near the volcano are to understand the real risks.

3. Pyroclastic flows are deadly

Pyroclastic flows are extremely hazardous and deadly. They were responsible for deaths in Pompeii and Herculaneum from the AD79 eruption of Vesuvius in Italy.

Even the famous volcanologists Katia and Maurice Kraft underestimated the reach of a pyroclastic flow during an eruption at Unzen volcano on June 3, 1991, which killed them along with many others.




Read more:
Curious Kids: Do most volcanologists die from getting too close to volcanoes?


Historic subduction zone volcanic eruptions producing devastating pyroclastic flows include:

  • Vesuvius, Italy AD 79
  • Tambora, Indonesia (1815)
  • Krakatau (Krakatoa), Indonesia (1883)
  • Mt Pelée, Caribbean (1902)
  • Mt St Helens, USA (1980)
  • Mt Pinatubo, Philippines (1991)
  • Unzen, Japan (1991).

At Fuego, the loose, fragmented volcanic material (known as tephra) lying on the slopes after eruptions may be remobilised by rain to form volcanic mudflows known as lahars. These pose a significant current and future risk for the people surrounding Fuego compared to those living in Hawaii.

Pyroclastic density currents were the main cause of death from volcanic activity in the 20th Century, killing around 45,000 people, almost 50% of all volcanic deaths in that time period (total deaths from volcanic activity is estimated to be 91,724).

While eyes are diverted toward eruptions in Central America and the Pacific Ocean, Indonesia has raised the alert level on some of its volcanoes this week. It now has 21 volcanoes on alert levels 2-4 (yellow, orange and red) on a scale of 1-4.

The ConversationLocal authorities will be vital in managing and communicating the risks of these volcanoes, as well as around Fuego and Kilauea.

Heather Handley, Associate Professor in Volcanology and Geochemistry, Macquarie University

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.




Read more:
Trouble in paradise: eruptions from Kīlauea volcano place the Hawaiian island on red alert


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.




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


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.

The ConversationLessons 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.