The eruption of the world’s largest active volcano – Mauna Loa in Hawaii – may soon come to an end, but its climate-related implications will be great because volcanic gases like sulphur dioxide can cause global cooling, while volcanic carbon dioxide, a greenhouse gas, has the potential to promote global warming …
Climate change is causing the widespread warming of our land, oceans, and atmosphere. Apart from this, it also has the potential to increase volcanic activity, affect the size of eruptions, and alter the “cooling effect” that follows volcanic eruptions. Any of these scenarios could have far-reaching consequences. Yet we do not fully understand the impact a warming climate could have on volcanic activity.
The Mauna Loa volcano, the largest active volcano in the world, has erupted for the first time in nearly 40 years. The eruption began on November 27, choreographing a dangerously spectacular display that sent rivers of molten rock gushing down its side and drawing crowds of spectators hoping to see the flowing lava in person. Though lava eruption from the last active fissure continues, the lava oozing down and the volcanic gas emissions have been greatly reduced. “High eruption rates will not resume based on past eruptive behaviour and current behaviour suggests that the eruption may end soon,” according to the US Geological Survey (USGS). “However, an inflationary trend of Mauna Loa’s summit is accompanying the decreased activity and there is a small possibility that the eruption could continue at very low eruptive rates. Most lava is confined to the vent in a small pond.” USGS added. Still, eruptions can be unpredictable and there is “the uncertainty of continuing eruptive activity and the possibility of volcanic ash emissions,” USGS cautioned. “The significance of the reduced supply of lava is not yet clear; it is common for eruptions to wax and wane or pause completely, but none of the eight recorded eruptions from Mauna Loa’s Northeast Rift Zone returned to high eruption rates after those rates decreased significantly,” USGS had previously said. David Phillips, deputy scientist-in-charge of the USGS Hawaiian Volcano Observatory, described the slowing volcano activity: “There is much less lava coming out. The lava channels below the fissure are mostly drained of lava at this point.” The eruption began in Moku'āweoweo, the summit caldera of Mauna Loa, around 11:30 a.m. on November 27, according to the Hawaii Volcano Observatory.
However, its eruption has given birth to another fear. Volcanoes can impact climate change. During major explosive eruptions huge amounts of volcanic gas, aerosol droplets, and ash are injected into the stratosphere. Injected ash falls rapidly from the stratosphere -- most of it is removed within several days to weeks -- and has little impact on climate change. But volcanic gases like sulfur dioxide can cause global cooling, while volcanic carbon dioxide, a greenhouse gas, has the potential to promote global warming.
Meanwhile, Mauna Loa’s erupting sister volcano – Kilauea – has been erupting since last year. Lava from Kilauea is, however, confined to a small pond near the top, and not gushing down the side. The two simultaneous eruptions created a rare dual-eruption event on the Big Island, according to Hawai’i Volcanoes National Park.
Sulfate aerosols can cool the climate and deplete Earth's ozone layer
The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulfur dioxide to sulfuric acid, which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth's lower atmosphere or troposphere.
Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The climactic eruption of Mount Pinatubo on June 15, 1991, was one of the largest eruptions of the 20th century and injected a 20-million-ton (metric scale) sulfur dioxide cloud into the stratosphere at an altitude of more than 20 miles. The Pinatubo cloud was the largest sulfur dioxide cloud ever observed in the stratosphere since the beginning of such observations by satellites in 1978. It caused what is believed to be the largest aerosol disturbance of the stratosphere in the twentieth century, though probably smaller than the disturbances from eruptions of Krakatau in 1883 and Tambora in 1815. Consequently, it was a standout in its climate impact and cooled the Earth's surface for three years following the eruption, by as much as 1.3 degrees F at the height of the impact. The large 1783-1784 Laki fissure eruption in Iceland released a staggering amount more sulfur dioxide than Pinatubo (approximately 120-million ton vs. 20). Although the two eruptions were significantly different in length and style, the added atmospheric SO2 caused regional cooling of Europe and North America by similar amounts for similar periods of time.
Do the Earth's volcanoes emit more CO2 than human activities? No.
Carbon dioxide (CO2) is a greenhouse gas and is the primary gas blamed for climate change. While sulfur dioxide released in contemporary volcanic eruptions has occasionally caused detectable global cooling of the lower atmosphere, the carbon dioxide released in contemporary volcanic eruptions has never caused detectable global warming of the atmosphere. In 2010, human activities were responsible for a projected 35 billion metric tons (gigatons) of CO2 emissions. All studies to date of global volcanic carbon dioxide emissions indicate that present-day subaerial and submarine volcanoes release less than a percent of the carbon dioxide released currently by human activities. While it has been proposed that intense volcanic release of carbon dioxide in the deep geologic past did cause global warming, and possibly some mass extinctions, this is a topic of scientific debate at present.
Published scientific estimates of the global CO2 emission rate for all degassing subaerial (on land) and submarine volcanoes lie in a range from 0.13 gigaton to 0.44 gigaton per year. The 35-gigaton projected anthropogenic CO2 emission for 2010 is about 80 to 270 times larger than the respective maximum and minimum annual global volcanic CO2 emission estimates. There is no question that very large volcanic eruptions can inject significant amounts of carbon dioxide into the atmosphere. The 1980 eruption of Mount St. Helens vented approximately 10 million tons of CO2 into the atmosphere in only 9 hours. However, it currently takes humanity only 2.5 hours to put out the same amount. While large explosive eruptions like this are rare and only occur globally every 10 years or so, humanity's emissions are ceaseless and increasing every year. There continues to be efforts to reduce uncertainties and improve estimates of present-day global volcanic CO2 emissions, but there is little doubt among volcanic gas scientists that the anthropogenic CO2 emissions dwarf global volcanic CO2 emissions.
That study used data from a NASA satellite, which provides water vapor measurements globally on a daily basis. Dr Vömel and his colleagues took a different approach, using data from instruments in small packages called radiosondes that are carried aloft by balloons. Radiosondes are launched on a regular timetable, usually every 12 hours, at weather stations around the world. This approach was only possible because there were regular balloon launches from Australia, Fiji and other locations that were close enough to the eruption that the instruments were carried into the volcanic plume. It also helped that the water vapour concentrations in the plume were extremely high. “Any self-respecting scientist who knows stratospheric water vapor knows you cannot measure it with radiosondes,” Dr Vömel said. “Don't even think about it. However, this event was so unbelievably huge.”
The eruption of an underwater volcano in the Pacific Ocean in January that was so large it produced a global shock wave also spewed huge amounts of water vapour into the upper atmosphere, where it may cause a small, short-term spike in global warming, scientists believed. The injection of what the researchers estimated was at least 55 million tons of water vapour into the stratosphere may also temporarily cause more depletion of the protective ozone layer in the atmosphere, they said. The eruption of the Hunga Tonga–Hunga Haʻapai volcano in the island nation of Tonga on Jan 15 was the largest in decades. It spawned a tsunami that devastated parts of Tonga, as well as smaller tsunamis thousands of miles distant that were caused by changes in air pressure as the shock wave circled the world. Because it occurred about 500 feet underwater, the eruption of superheated molten rock also caused seawater to flash explosively into steam. A plume of water vapour, volcanic gases and ash reached an altitude of 35 miles. That increased the amount of water vapour in the stratosphere, which ends at an altitude of 31 miles, by at least 5 percent. “It’s absolutely unique,” said Holger Vömel, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo. “This has not happened since we’ve been capable of measuring stratospheric water vapour, which started something like 70 years ago.”
Dr Vömel said any estimate of the amount of additional warming that the Tonga eruption would add was highly speculative at this point. “But I wouldn’t be surprised if it was the same order of magnitude” as Pinatubo, he said, just in the opposite direction. The extra warming would likely continue for longer than the cooling after Pinatubo, he added. Susan Solomon, an atmospheric scientist at the Massachusetts Institute of Technology who described the temperature impacts of changes in stratospheric water vapor in a 2010 study, said the Tonga eruption “could add something on the order of 0.05 degrees of warming to global average temperatures,” probably for three to five years. “That’s less than what we expect from carbon dioxide, which is closer to 0.1 to 0.2 degrees per decade,” she said. All that water vapour will very likely also alter the atmospheric chemistry that destroys ozone, the oxygen molecule that protects life on Earth from harmful ultraviolet radiation from the Sun. “By increasing the amount of water vapour drastically, that should decrease the amount of ozone,” Dr. Vömel said. But that would be temporary, he said, because ozone formation and destruction “is a cycle that keeps going.” Dr. Solomon said that any loss of ozone near the boundary of the stratosphere and the lower atmosphere would also quite likely lead to some surface cooling, which would counteract the warming from the added water vapour. The study estimated the amount of water vapour injected by the Tonga eruption to be about three times higher, at about 160 million tons.
Meanwhile, the Fagradalsfjall volcano in Iceland began erupting again after eight months of slumber – so far without any adverse impacts on people or air traffic. The eruption was expected. It is in a seismically active (uninhabited) area, and came after several days of earthquake activity close to the Earth’s surface. It is hard to say how long it will continue, although an eruption in the same area last year lasted about six months.
Cold volcanic regions
Now, let us take a look at volcanic regions covered in ice. There is a long-established link between the large-scale melting of ice in active volcanic regions and increased eruptions. Research on Iceland’s volcanic systems has identified a heightened period of activity related to the large-scale ice melt at the end of the last ice age. The average eruption rates were found to be up to 100 times higher after the end of the last glacial period, compared to the earlier colder glacial period. Eruptions were also smaller when ice cover was thicker. But why is this the case? Well, as glaciers and ice sheets melt, pressure is taken off Earth’s surface and there are changes in the forces (stress) acting on rocks within the crust and upper mantle. This can lead to more molten rock, or “magma”, being produced in the mantle – which can feed more eruptions. The changes can also affect where and how magma is stored in the crust, and can make it easier for magma to reach the surface. Magma generation beneath Iceland is already increasing due to a warming climate and melting glaciers. The intense ash-producing eruption of Iceland’s Eyjafjallajökull volcano in 2010 was the result of an explosive interaction between hot magma and cold glacial melt water. Based on what we know from the past, an increase in Iceland’s melting ice could lead to larger and more frequent volcanic eruptions.
But what about volcanic regions that are not covered in ice – could these also be affected by global warming? Possibly. We know climate change is increasing the severity of storms and other weather events in many parts of the world. These weather events may trigger more volcanic eruptions. On December 6 2021, an eruption at one of Indonesia’s most active volcanoes, Mount Semeru, caused ashfall, pyroclastic flows and volcanic mudflows (called “lahars”) that claimed the lives of at least 50 persons. Local authorities had not expected the scale of the eruption. As for the cause, they said several days of heavy rain had destabilised the dome of lava in the volcano’s summit crater. This led to the dome collapsing, which reduced pressure on the magma below and triggered an eruption. Signals of volcanic unrest are usually obtained from changes in volcanic systems (such as earthquake activity), changes in gas emissions from the volcano, or small changes in the shape of the volcano (which can be detected by ground-based or satellite monitoring). Predicting eruptions is already an incredibly complex task. It will become even more difficult as we begin to factor in risk posed by severe weather which could destabilise parts of a volcano.
Five of the most significant volcanic eruptions in history
1. The first recorded volcanic eruption: Vesuvius (79 AD)
On August 24, 79 AD, Mount Vesuvius erupted, releasing plumes of toxic gas that asphyxiated some 2,000 people in the nearby town of Pompeii. A torrent of volcanic debris cascaded on the settlement, entombing it beneath a blanket of ash. All in all, it took just 15 minutes for Pompeii to disappear. But for millennia, the Lost City waited. Then, in 1748, a surveying engineer rediscovered Pompeii for the modern world. And having been sheltered from moisture and air beneath layers of ash, much of the city had barely aged a day. Ancient graffiti was still etched on the walls. Its citizens lay frozen in eternal screams. Even blackened loaves of bread could be found in the bakery’s ovens. The eruption of Vesuvius on that fateful day in 79 AD was witnessed by Roman author Pliny the Younger, who described the volcano’s “sheets of fire and leaping flames” in a letter. Pliny’s eyewitness account makes Vesuvius possibly the first formally documented volcanic eruption in history.
2. The longest volcanic eruption: Yasur (1774-present)
When Vanuatu’s Yasur volcano started erupting back in 1774, Britain was ruled by George III, the United States did not even exist and the steamship was yet to be invented. But that same eruption is still going to this day – more than 240 years later. That makes Yasur, according to the Smithsonian Institution’s Global Volcanism Program, the longest volcanic eruption in modern history. Back in 1774, Captain James Cook happened to be passing through Vanuatu on his travels. He witnessed the start of Yasur’s enduring eruption first-hand, watching as the volcano “threw up vast quantities of fire and smoke and made a rumbling noise which was heard at a good distance.” Modern visitors to Vanuatu’s island of Tanna can still witness Yasur’s perennial pyrotechnics display for themselves. The volcano’s peak is reachable on foot, so thrill seekers can even trek up to the crater’s edge – if they dare.
3. The deadliest volcanic eruption: Tambora (1815)
The 1815 eruption of Mount Tambora was the deadliest volcanic eruption in recorded history, as well as the most powerful, and it caused a devastating chain of events. The deadly saga started on Sumbawa – an island now in Indonesia – with the most powerful volcanic blast ever documented. Tambora released a blinding flurry of fire and destruction that instantly killed 10,000 islanders. But the situation grew worse from there. Tambora threw ash and noxious gases some 25 miles high into the stratosphere, where they formed a thick smog. This haze of gas and debris sat above the clouds – blocking the sun and forcing rapid global cooling. So began 1816, the ‘year without a summer’. For months, the northern hemisphere was plunged into an icy grip. Crops failed. Mass starvation soon followed. In Europe and Asia, disease ran rife. Ultimately, around 1 million people are estimated to have died in the extended aftermath of Mount Tambora’s eruption. It was, in more ways than one, a truly dark time for humanity.
4. The loudest volcanic eruption: Krakatoa (1883)
When Indonesia’s Mount Krakatoa erupted on August 27, 1883, it was the loudest volcanic eruption ever recorded. It was also the loudest sound in known history. Nearly 2,000 miles away in Perth, Australia, the Krakatoa eruption resonated like gunfire. Its sound waves circled the Earth at least three times. At its loudest, the Krakatoa eruption reached roughly 310 decibels. The bombing of Hiroshima during WWII, by comparison, reached less than 250 decibels. Krakatoa was also the deadliest volcanic eruption of the last 200 years. It triggered tsunami waves some 37 metres tall and killed at least 36,417 people. The eruption rocketed plumes of ash into the atmosphere which turned skies red across the globe. In New York, firefighters were called to extinguish blazes that couldn’t be found. The scarlet skies depicted in Edvard Munch’s The Scream might even owe their red hue to the Krakatoa eruption.
5. The most expensive volcanic eruption: Nevado del Ruiz (1985)
The eruption of Colombia’s Nevado del Ruiz volcano in 1985 was relatively small, but it caused untold destruction. “Nevado” translates to “topped with snow”, and it was this glacial peak that proved most devastating for the region. Its ice melted during the eruption. Within hours, devastating lahars – mudslides of rock and volcanic debris – tore through the surrounding structures and settlements. Schools, homes, roads and livestock were all obliterated. The entire town of Armero was flattened, leaving 22,000 of its citizens dead. The Nevado del Ruiz eruption also came at a great financial cost. Taking into consideration the immediate destruction of property – as well as far-reaching impacts like the hampering of travel and trade – the World Economic Forum estimates that the Nevado del Ruiz eruption cost around $1 billion. That price tag makes Nevado del Ruiz the most expensive volcanic incident in recorded history – surpassing even the 1980 eruption of Mount St. Helens in the USA, which cost around $860 million. In 1783 a massive eruption of Lakagígar volcano nearly forced the abandonment of Iceland as 15 cubic kilometres of lava was blown into the air. The effects of this eruption caused enormous death and destruction in Iceland but also led to the failure of crops across northern Europe causing the deaths of 25,000 people and helping to cause the French revolution. Dan spoke to Páll Einarsson, from the Institute of Earth Sciences, University of Iceland, about the history of Iceland's volcanoes and how their presence continues to be felt both in Iceland and around the world.