The new era of volcanology

Kilauea is considered by many experts the most active volcano in the world. That is why it is also one of the most studied using sensors and other instruments. During the eruption that began on May 3, 2018 and lasted for three months, a torrent of information was collected that will keep volcanologists busy for decades. There is a before and after to this historic, spectacular and very destructive eruption. In the first days, an earthquake of magnitude 6, 9 on the Richter scale was unleashed that caused the southern flank of the volcano to slide 5 meters and produced 24 cracks that emitted a cubic kilometer of lava flows and destroyed more than 700 houses. But what most caught the attention of scientists was the formation of a caldera on the summit. By caldera is understood a huge crater formed, when the ground collapses, on the magma pocket of the volcano. It is the magma reservoir that is being emptied by the eruption. In the Kilauea, a new caldera 500 meters deep by 1.8 km wide and 2.8 km long emerged within a larger and older one that was created around the year 1500.

The largest eruptions occur when THE calderas collapse, so it is crucial for volcanologists to understand their formation. The process had been observed before, but never in such detail. As a pocket of magma empties as it fuels the eruption, it deflates like a balloon until the reservoir roof gives way and progressively sinks. In the case of the Kilauea, geophysicist Kyle Anderson of the United States Geological Survey (USGS) believes that no one expected the landslide to start when only 4% or less of the magma had been expelled, much earlier than previously thought. for these processes. In addition, the eruption and the definitive collapse ended when only between 11% and 33% of the magma had been emptied, according to the mathematical model, which implies that Kilauea still contains a large amount of magma inside. Another important piece of information is that the process is episodic: the eruption causes the pressure within the magmatic reservoir to decrease until the ceiling collapses which, when hitting the reservoir, increases the pressure again and reactivates the eruption, which returns to low r pressure, and so on over three months.

The top of the Kilauea volcano has been occupied on multiple occasions by a lava lake, considered in Hawaiian legends the home of the goddess Pele. But in July 2019, water was sighted deep within the new crater. The bottom of the caldera had dropped below the water table and the groundwater formed a lake that continues to grow and deepen today. Water in a volcano crater is a bad combination. Kilauea was said to be the safest volcano in the world, as its quiet eruptions rarely endangered human lives, as it was easy to escape the lava flow simply by walking, as seen in some documentaries.

This perception has changed. The USGS geologist Don Swanson, in his study of ancient eruptions of the volcano, has revealed a cyclical condition in its activity, which alternates calmer phases of lava flows, fountains and lakes with other more violent ones, based on explosive eruptions that they send ash plumes and dangerous pyroclastic flows, gas currents, and extremely high-temperature volcanic material moving at hurricane-force speeds. The requirement for explosive eruptions has been inferred through various geological investigations: that the caldera be deep enough to hold water, which has just been met in the case of Kilauea. Hence, volcanologists suspect that this Hawaiian mountain will enter a phase of explosive eruptions in the near future.

New times are also being experienced in eastern Java, where one of the icons of volcanism is located, el Krakatoa, today known as Anak Krakatau. This Indonesian volcano has a bad reputation since in 1883 it starred in one of the largest eruptions in history that left more than 35,000 deaths. The island that was then collapsed under the sea in the Sunda Strait, between Java and Sumatra, and formed an underwater caldera. The Anak Krakatau, which means ‘son of Krakatoa’, emerged from the waters in 1926 and has since grown to a cone 338 meters high in 2018.

In a 2012 study, Thomas Giachetti, from the University of Oregon (USA), already identified that Anak Krakatau is unstable. Rising over the steep rim of the 1883 undersea caldera, it risks the young mountain’s flank sliding to the bottom at any moment. Giachetti ran a simulation and saw that if it occurred, the event would launch a tsunami against the coasts of Java and Sumatra in less than an hour. But even though the risk is known, the volcano was not properly monitored. And so, on December 22, 2018, a tragedy very similar to the one Giachetti had foreseen took place. During the night, 0.2 km 3 of the flank of the volcano broke off and a tsunami swept through Java and Sumatra with a toll of 430 dead and more than 10 000 injured.

Volcanoes, by emitting lava, gradually form a mountain known as a volcanic building. As we know, any building that is poorly constructed collapses. Volcanoes tend to be unstable constructions, as the pressure of the magma that pushes from within complicates things and makes landslides one of the most important risks. The eruption of Saint Helena in Washington state in 1980 sparked interest in these phenomena in scientists. That day, an avalanche of rocks uncorked a pocket of magma and pressurized gases that was ejected laterally at supersonic speed. To the east it struck Spirit Lake, displacing the water in a tsunami that reached 260 m above the lake, and advanced westward 26 km through a valley, burying everything in its path under a 45-foot layer of debris. m thick.

But as impressive as the St. Helena’s side collapse was, it pales when compared to some mega-landslides on oceanic islands like Hawaii, with rock volumes more than a thousand times greater. There are many volcanoes susceptible to sliding, such as Stromboli, off Sicily, Pacaya in Guatemala or Pico in the Azores archipelago. In all of them a movement of the slope is detected that shows a large block separated from the volcanic building. Stromboli and Peak could produce a tsunami.

Planet Earth has more than 1,400 active volcanoes. Keeping them all in check to prevent disasters is a huge challenge. Only a few have an adequate set of instruments to measure seismic activity, volcanic gases or deformation, which is a key parameter. The processes that take place within a volcanic system – movement, crystallization or degassing of magma … -, as well as landslides, fault displacement or swelling when receiving magma from the depths, are reflected by changes in the shape of the earth’s surface.

volcanic deformation

There is a satellite remote sensing system to monitor volcanic deformation. Satellites can play a revolutionary role in volcanology, as they allow global measurements of remote volcanoes and for countries that do not have good monitoring networks. The InSAR technique stands out, which uses microwave radiation to detect changes in distance from the Earth’s surface. The advantage of electromagnetic radiation is that it also works at night and is capable of penetrating clouds. By comparing a time series of many radar images, a deformation map is created called an interferogram.

Interferograms have become a key monitoring tool, as they can measure the deformation of almost all volcanoes with a resolution of millimeters or centimeters. But it is difficult to discriminate the relevant information from the huge amount of data they handle. In 2019, a team led by geoscientist Matthew Gaddes, from the University of Leeds (England), did a study with artificial intelligence to warn about volcanoes in a state of agitation and has shown promising results. On-board satellite sensors allow us to measure, for example, the thermal radiation of a volcano or detect the concentration of sulfur dioxide, a very abundant compound in volcanic clouds that is used to estimate its possible climate impact or prevent risks in aviation. In order to predict eruptions, volcanologists listen to certain seismic signals, volcanic gases or the degree of deformation of the ground. The causes of the landslides were almost unknown due to their rarity.

However, the eruption of Anak Krakatau has helped advance the understanding of these dangerous phenomena. An international research team led by Thomas Walter, a geophysicist at the German Research Center for Geosciences, studies the catastrophe using multiparametric data, both satellite and from measuring instruments in the vicinity of the volcano, and tries to identify a cascade of previous precursor factors. In early 2018, InSAR analysis detected that the flank of the volcano was deforming at a rate of 4 mm per month. A part of the island had detached itself from the rest of the volcano and was sliding over a fault towards the sea, which heralded a lateral collapse. In June of the same year an intense eruption was activated that lasted six months until the final landslide. Sensors on satellites captured a flow of thermal energy a hundred times greater than the volcano’s average during the previous eighteen years. The rate of flank deformation accelerated to 10 mm per month during this eruption. On December 22, 2018, the day of the catastrophe, it began with eruptive activity followed by a period of calm. Two minutes before the landslide, an earthquake occurred. The landslide produced a strong characteristic seismic signal. As seismic waves travel faster than the tsunami, this signal could have been used as a short-term precursor. The results of this research will contribute to creating more accurate tracking systems for volcanoes with unstable flanks.

Other research by Lingling Ye, from the University of California at Santa Cruz (USA), published in January 2020 in Science Advances, proposes the creation of an early warning system for volcanogenic tsunamis similar to the one that already exists for tsunamis seismogenic, through the detection of seismic signals, similar to those recorded on December 22, that accompany the landslide.

Regarding Anak Krakatau, where there was a symmetrical cone before, there is now a large open crater to the west, the direction in which it collapsed. The island has lost height: from 338 meters to 120, although the volcano has already begun to rebuild. The last eruption was on April 11, 2020 with spectacular lava fountains and a column of ash that rose 15 kilometers high. The Anak Krakatau remains very active, and in time it is likely that it will grow back as a mountain. But for the moment it is relatively harmless and volcanologists turn their gaze elsewhere.

one of the most studied by remote sensing is the Laguna del Maule supervolcano, due to the rapid inflation of its caldera. The eruptions of these types of giant calderas can have an extraordinary global effect. The Laguna del Maule is in the Chilean Andes and went unnoticed until it woke up in 2004. Three years later, the area of ​​the lagoon began to rise, filling with magma at a rate of 28 cm a year. This far exceeded that observed in other volcanoes in the world. Today it continues to grow at more than 20 cm per year, which worries many volcanologists. Furthermore, instead of a mountain, what we find in this supervolcano is a ring of multiple volcanic mouths that surround a lake and form a large 15 km by 25 km caldera. Its lavas are of the rhyolitic type.

Magmas are not all the same, some are viscous and others more fluid. Fluids, like basalt, behave less explosively, more calm. It would be the case of the Kilauea if it weren’t for an external factor – water – causing a great explosion. At the other extreme was rhyolite, a relatively unusual and highly explosive magma. The large rhyolitic calderas are the ones that arouse the most interest in volcanology. When the magmatic reservoir of one of these systems collapses and forms a new caldera, a gigantic eruption takes place that spews hundreds or thousands of cubic kilometers of volcanic ash and impacts the global climate. That is why they are called supervolcanoes. Fortunately, large calderas only collapse a few times over their million-year lifetimes, and their usual eruptions are smaller. The last to emit more than 1000 km 3 of volcanic material was carried out by the Taupo, in New Zealand, 25,000 years ago. Hopefully it may take several thousand years for such an eruption to repeat itself!

Earth currently has about 1,400 active volcanoes. Below we have pointed out the most significant or violent, among which the Hawaiian Kilauea stands out. Below we can see what this volcanic system is like inside, which has intrigued volcanologists since it exploded with virulence in May 2018. Various scientific teams are working in situ or from satellites to study its processes.

Volcanic clouds emitted in explosive eruptions can reach the stratosphere. And it is there where gases such as sulfur dioxide and hydrogen sulfide, through chemical processes, are transformed into aerosols that reflect part of the solar radiation and produce a cooling effect on the planet’s surface. The largest volcanic eruptions have produced a drop in temperature large enough to cause global damage and have been associated with the incidence of epidemics and famines due to crop failure. A famous case was the Tambora eruption in Indonesia in 1815, which made 1816 known as the year without a summer. The skies turned gray and pale, as reflected by many painters of the time.

In 2016, Cambridge University geographer Ulf Büntgen discovered a volcanic winter of much greater proportions from climatic records that have been reflected in tree rings in Russia’s Altai Mountains. Two powerful eruptions took place in the years 536 and 540, which triggered a winter episode during which the most intense cold season of the last two thousand years in Asia and Europe occurred. Temperatures in Central Asia dropped 4 degrees Celsius in the years following the 536 eruption and did not fully recover until 660. This period is called the Little Ice Age of ancient times.

The decline of an empire. Just at that moment in history, the Byzantine Emperor Justinian had led the Eastern Roman Empire to a rapid expansion, which was slowed down by that freezing weather episode that inaugurated a time of bad harvests, famines and pandemics. There was also what is known as the Justinian plague, which ravaged the Eastern Roman Empire between 541 and 543 and was probably caused by the bacterium Yersinia pestis. Between 25 and 50 million people died in Europe, Asia and Africa. Its impact was especially cruel with the Byzantine Empire, which began a progressive decline as its depleted armies could not maintain the borders established in 540.

Volcanologists wonder which volcanoes to blame for these two eruptions. Geoscientist Robert Dull, from the University of Texas Institute of Environmental Sciences, published a study in 2019 in which he identifies Ilopango, in El Salvador, as the volcano responsible for the 540 eruption. This explosion took place in Central America in the middle Mayan Empire and it is estimated that it produced one hundred thousand deaths by direct effects. For its part, the identity of the volcano from the 536 eruption is still a mystery to scientists.

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