Recent eruptions

Volcanoes and earthquakes are dramatic examples that the Earth is a living, dynamic planet. Unfortunately, because much of what was understood of these phenomena was faulty, including inadequate descriptive techniques, most records of specific eruptions written before 1800 are now of limited value. Since then, however, a number of particularly instructive examples have emerged.

Tambora

Located on the island of Sumbawa, about 160 kilometers east of Java, Tambora volcano erupted in April 1815, however the exact date and preliminary activity are unknown. This is believed to be the most powerful volcanic eruption of modern times. There were no surviving eyewitnesses, as virtually the entire population of Sumbawa was killed as a result. The noise of the explosion was heard 1,500 kilometers (932 miles) away, and its atmospheric effects were felt worldwide. As clouds of volcanic ash circulated throughout the stratosphere, 1816 became in America and Europe “the year without a summer,” during which normal harvests were greatly curtailed.

Graham Island

Another otherwise unremarkable Vesuvian eruption of October 22–26, 1822, along with a predecessor in 1818, prompted George Julius Poulett Scrope to study the volcanoes of Europe. His Considerations on Volcanoes (1825) inaugurated the modern science of volcanology. Graham Island was an underwater submarine volcano that appeared off the southern coast of Sicily for several months in 1831, only to disappear by year's end. As the first volcano of any kind to be observed almost daily throughout its existence, it was considered by such European geological theorists as Scrope and Sir Charles Lyell to be an example of fundamental importance in their debates regarding the formation of volcanoes. The forceful eruption of Vesuvius from April 24–30, 1872, stimulated Luigi Palmieri, the director of the Volcano Observatory on the slopes of Mount Vesuvius, to formulate his influential theory that volcanic eruptions are often characterized by predictable phases. This eruption was also the first major eruption to be photographed.

Krakatau was a three-part volcanic island located between Java and Sumatra. After preliminary activity beginning on May 20, 1883, it violently erupted on August 26 and 27. This eruption was audible from nearly 5,000 kilometers (3,107 miles) away. An ensuing tsunami generated by the volcano killed more than 36,000 people. As with Tambora, subsequent environmental effects were felt globally, generating much scientific and popular interest. This prompted Dutch and British investigators to publish important studies.

Tarawera

Following some preliminary earthquakes, the top of domelike Mount Tarawera, on the North Island of New Zealand, split apart on June 10, 1886, exposing the internal structure of the dome and creating a series of steam-blast craters. When fissuring extended beneath Lake Rotomahana, further steam explosions followed, destroying two world-famous hot-spring formations, the White and Pink terraces. Ash and mud from the eruption buried several Maori villages and killed more than 140 people.

Bandai-san

After more than one thousand years of relative inactivity, Bandai-san volcano, located on the island of Honshu in Japan, erupted without warning on July 15, 1888. The initial event lasted for less than two minutes. Nonetheless, the north slope of the mountain was demolished, burying the villages and people of an entire valley with avalanches and mudflows. Although only a steam explosion, it was the worst volcanic disaster in the history of Japan.

La Soufrière

La Soufrière at the northern end of the island of St. Vincent in the West Indies became active on May 6, 1902, creating a crater lake in a series of mudslides. Its major eruption, on May 7, was the first in modern times where glowing avalanches of gas, ash, and lava (nuées ardentes) were recognized. These materials sped down all sides of the mountain, however, they caused little damage. The thrust of the eruption had been vertical, with the glowing avalanches on its slopes a secondary phenomenon caused only by fallout and gravity. Activity continued into March 1903.

Mount Pelée

Nearby Mount Pelée, located on the island of Martinique, was active from April 24, 1902, until October 5, 1905. This was repeated from September 16, 1929, to December 1, 1932. After giving ample warning, the volcano erupted violently on May 8, 1902, one day after Soufrière on St. Vincent. The nueés ardentes was, this time, ejected straight down the western slope of the volcano. The searing, suffocating clouds of gas and ash rushed like an avalanche to engulf the city of St. Pierre. This led to its destruction and the death of about thirty thousand people, or all but a handful of its former citizens. Second only to the destruction of Pompeii by the Vesuvius eruption in 79 CE, this volcanic disaster was the most famous of modern times. It greatly stimulated interest in volcanoes and attracted two major figures to their study—Thomas A. Jagger and Frank A. Perret. It also postulated a new type of eruption called the Peléan and initiated a dispute regarding nuées ardentes where evidence from its own later eruptions would help resolve.

Santa María

The Santa María volcano in the Sierra Madre in Guatemala was dormant for approximately five hundred years before it had its first recorded eruption on October 24, 1902. A seismic swarm began in January 1902, indicating the volcano's increasing activity and causing a major earthquake in April. The volcano ejected roughly 5.4 cubic kilometers (1.3 cubic miles) of magma, making it the second largest eruption of the twentieth century with a Volcanic Explosivity Index (VEI) of 6. An estimated five thousand people were killed by the Santa María eruption.

Alaskan Eruptions

Accounts of a major Alaskan Peninsula eruption from June 6 to June 9, 1912—the most powerful modern one on the North American continent and the largest eruption of the twentieth century—differ with age. Current understanding is that the primary effusion radiated from a newly formed volcano named Novarupta on the flank of Mount Katmai rather than from Katmai itself. Explosions were heard 1,000 kilometers (621 miles) away. Ash fell thickly at a distance of 160 kilometers (100 miles), and an adjacent valley floor was transformed into a steaming fumarolic basin. This became known as the Valley of Ten Thousand Smokes. The old crater of Mount Katmai later collapsed, perhaps because the liquid rock, or magma, underlying it had shifted. Aside from its forcefulness, Katmai is significant for being the only example of an ignimbrite, or fused rhyolite tuff, eruption in modern times.

Lassen

Lassen Peak, located in Lassen Volcanic National Park in Northern California, is, like Tarawera, a volcanic dome, and one of the largest known. Long dormant, it resumed activity on May 30, 1914, becoming particularly violent one year later, from May 19 to May 22, 1915. When directional nuées ardentes coursed down its shattered slopes to devastate whole forests and create powerful mudslides. Some less important lava flows then followed, with activity continuing into 1917. Prior to the eruption of Mount St. Helens in 1980, the 1915 eruptions of Mount Lassen were the most famous recent ones to have taken place within the United States.

Parícutin

Parícutin emerged overnight from a cornfield in central Mexico on February 20, 1943. This fragile but rapidly growing cinder cone reached a height of 50 meters the next day; lava began flowing from its base rather than its crater, destroying a nearby farm. In June 1944, it buried an entire village.

Hekla

Hekla, the best-known Icelandic volcano, erupted memorably on March 29, 1947, after more than one century of dormancy. Large amounts of ash and other debris were ejected from a fissure, and lava flows poured down the volcano's slopes from a series of fissure-related vents. After nearly thirteen months of continuous activity, which ended on April 21, 1948, approximately 1 billion cubic meters of lava had been discharged, in addition to immense volumes of ash. Eruptions of this type do not usually endanger human life, but Iceland's livestock and farming industries were severely affected, both from the destruction of arable land and from the widespread emissions of toxic gases. Considerable eruptions at Hekla also occurred in 1991 and 2000.

Lamington

Prior to 1951, Mount Lamington, on the northern side of Papua New Guinea, was considered regarded as extinct. It consisted of a deeply eroded complex of volcanic domes, with heavy forestation and no record of previous activity. On January 15, however, earthquakes and emissions began, and then gradually intensified. The major eruption took place on May 21, featuring a huge eruption cloud and glowing avalanches of the St. Vincent type. These avalanches devastated an area of more than 230 square kilometers (89 square miles) and killed about six thousand people. Later eruptions were of the Vulcanian type and did not feature glowing avalanches but generated mudflows. The volcano's activity continued into 1956 and culminated in dome-building.

Bezymianny

Bezymianny (“no name”), in Kamchatka, was also thought to be extinct. After one month of seismic activity, eruptions began on October 22, 1955. The most violent blast, on March 30, 1956, destroyed the top 200 meters (656 feet) of the volcano and most of one side. Nuées ardentes, followed by huge ash and pumice flows, rushed down adjacent valleys. Dome formation then concluded the volcano's activity, all of which was meticulously recorded by Soviet volcanologists at a nearby observatory. After 1956, mild activity occurred, but the recurrence of lava flow and rest all but filled the crater. In 2016, though, the volcano began another eruption period that continued and demonstrated growth. On March 15–16, an explosion occurred that included ash plumes, avalanches, pyroclastic flows, and dome incandescence. A few months later, on May 28, 2022, the volcano exploded again, producing a plume of over 15 kilometers (49,000 feet) high. Again, on April 7, 2023, Bezymianny erupted, this time producing a plum of 12 kilometers (40,000 feet).

Ilha Nova, I and II

The Azores are a group of volcanic islands in the north Atlantic Ocean. A new vent adjacent to the island of Fayal opened on September 27, 1957, creating the island volcano of Capelinhos. Called Ilha Nova I (“new island”) this body of land existed for only a half month before disappearing, similar to Graham Island in 1831. On November 7, Ilha Nova II appeared, soon joining the island of Fayal in forming a new peninsula. It then fell into dormancy after little more than one year of activity. The resulting cone resembles others, such as Diamond Head in Hawaii, formed by underwater explosive eruptions.

Surtsey

One of best-studied underwater eruptions occurred on Surtsey, a newly created island in the Westman Islands off the southern coast of Iceland. Named for a fire giant in Norse mythology, Surtsey announced its presence with undersea turmoil on November 14, 1963. An island appeared the next day and grew rapidly, with every step in its progress being closely observed. The main vent became inactive for a time, beginning May 7, 1965, but two associated ones then spewed up smaller independent islands named Syrtlingur and Jolnir. Both subsequently disappeared. All activity ended on June 5, 1967, yet Surtsey continues to be of scientific interest as ecologists note its increasingly diverse complement of plant and animal life. In 2008, the United Nations Educational, Scientific, and Cultural Organization declared Surtsey a World Heritage Site for its great scientific value.

Heimay

Heimay (“home island”) is the largest and most permanent of the Westman Islands, the same group to which Surtsey belongs. It is approximately five thousand years old but had never been known to erupt. On January 23, 1977, however, a 2-kilometer (1.2-mile) fissure opened at the edge of the major town, whose five thousand inhabitants were then evacuated. The new vent, Eldfell, quickly developed a cone and poured lavas down into the deserted village, eventually destroying more than three hundred homes. Accumulations of heavier-than-air noxious gases made salvage operations hazardous and endangered farm animals, many of which had to be destroyed. While various attempts to impede the encroaching lava achieved only limited success, the volcano stopped of its own accord on June 28.

Mount St. Helens

After erupting nine times between 1831 and 1857, Mount St. Helens, in the state of Washington, was dormant until March 27, 1980, when significant activity began. The major eruption of May 18 blew off the top of the mountain and was said to be the most forceful in the contiguous forty-eight states during modern times. Mudslides triggered by the eruption then destroyed bridges, logging camps, homes, and thousands of trees. About sixty people perished. Further eruptions followed on May 25, June 12, July 22, and August 7, with occasional activity thereafter. These volcanic eruptions were the first in the contiguous United States since those of Mount Lassen. They attracted immense popular interest and were closely monitored by scientists.

El Chichón

In a now-familiar pattern, El Chichón volcano, in northern Chiapas, Mexico, awoke from a prolonged dormancy to erupt without warning on March 28, 1982. At least ten people who fled into a local church died when earthquakes demolished the building. Others were killed by falling debris and molten rock. A long ash cloud rained cinders across southern Mexico. Later eruptions in April left more people dead and homeless; survivors were then evacuated. Little had previously been known about this hitherto inactive killer.

Until 1991, Mount Pinatubo in the northern Philippines had no recorded eruptions. This was suddenly changed by the second-largest eruption of the twentieth century. More than three hundred people were killed by the eruption, but loss of life would have been much greater had the region had not previously been evacuated.

Soufrière Hills

The Soufrière Hills of the island of Montserrat in the Caribbean Sea consist of a stratovolcano, the first eruption of which began in 1995. Pyroclastic flows were produced, and more than six thousand people were evacuated to the north of the island.

Puyehue–Cordón Caulle

The eruption of the volcanic fissure Puyehue–Cordón Caulle on June 4, 2011, marked the largest eruption of the twenty-first century to date, with a Volcanic Explosivity Index of 5 ("paroxysmic"). Puyehue–Cordón Caulle's eruption occurred after more than fifty years of inactivity. More than three thousand people were evacuated from the surrounding areas, preventing any potential fatalities. The resultant ash cloud, containing an estimated one hundred million tons of debris, reached Cape Town, Africa, and Auckland, New Zealand, causing worldwide air travel disruptions as it circled the globe.

Hunga

In January 2022, the Hunga volcano in Tonga erupted, marking the largest eruption of the twenty-first century at the time. Beginning in December 2021, the submarine volcano in the Southern Pacific Ocean caused tsunamis in Tonga, Fiji, American Samoa, Vanuatu, and in several places along the Pacific rim.

Mount Ruang

On April 16, 2024, Mount Ruang in North Sulawesi, Indonesia, began erupting and prompted the evacuation of nearly 12,000 people, both from the island of Ruang and the nearby island of Tagulandang. The Indonesian government declared a state of emergency that lasted fourteen days and cited the volcano's alert level at a four, the highest possible. A tsunami warning was also issued, and the Sam Ratulangi International Airport in Manado closed. Though activity subsided briefly, on April 30, the volcano erupted again, and residents of both Ruang and Tagulandang once again had to evacuate. The plume rose to 1,000 kilometers (620 miles) and covered the entirety of Borneo.

A Small Sampling

Although these eruption episodes are among those most likely to appear in discussions of modern volcanism—either because of their historical significance or because of the thoroughness with which they were observed—it would be extremely misleading to suggest that they include most, or even the most typical, examples. Thousands of eruptions take place every year, most of which scientists know nothing about because the volcanoes remain hidden within the depths of the oceans. There are still remote areas on the earth, moreover, in which even a moderate land-based eruption might go unnoticed and, therefore, unrecorded.

Among the volcano records that do exist, all of the following have erupted twenty times or more since 1800: the three classic Italian volcanoes, Vesuvius, Stromboli, and Etna; Nyamuragia in Africa; Karthala (Grand Comoro) and Piton de la Fournaise (Réunion) in the Indian Ocean; White Island, Tarawera, Tongariro, Ngauruhoe, and Ruapehu in New Zealand; Bam and Manam, New Guinea; Ambrym and Lopevi, New Hebrides; Marapi and Dembo, Sumatra; Anak (“son of”) Krakatau, between Sumatra and Java; Gedeh, Gunter, Slamet, Merapi, Semeru, Tengger, Lamogan, and Ruang, Java; Batur, Bali; Soputan and Lokon-Empung, Sulawesi; Apu Siau, Sangihe Islands; Gamalama, Halmahera; Mayon and Taal, the Philippines; Sakura-jima, Kirishima, and especially Aso, Kyushu; Yake-Dake, Asama, Zao, and Iwake, Honshu; Oshima, Izu Islands; Komaga-Take and Taramai, Hokkaido; Karymsky and Kliuchevskoi, Kamchatka; Akatan and Shishadlin, Aleutian Islands; Pavlof, Alaskan peninsula; Kilauea and Mauna Loa, Hawaii; Colima, Mexico; Fuego, Guatemala; Izalco and San Miguel, El Salvador; Cerro Negro and Masaya, Nicaragua; Poas and Irazu, Costa Rica; Purace, Colombia; Reventador, Cotopaxi, and Sangay, Ecuador; Fernandina, Galápagos; and Rupungatito, Llaima, and Villarrica, Chile. It will be noted that a number of the most famous volcanoes do not appear; they have erupted either less frequently or not at all since 1800.

Study of Volcanic Eruptions

Broadly speaking, data relevant to any given volcanic eruption fall into three separate but related categories, depending upon whether they were collected prior to, during, or after the eruption. Data collected prior to an eruption include the previous eruptive history of the volcano: the types, the frequency, and the magnitude of its known eruptions. Illuminating as this information can be, however, it has not been shown to have reliable predictive value. Yet a volcano on the verge of eruption will often signal its upcoming behavior in a variety of ways. These include increased fumarolic activity, changes in the chemistry of associated waters, seismic disturbances, and tumescence (swelling). Certain changes in electrical and magnetic phenomena have been noted as well. Volcanologists, therefore, monitor all of these indicators carefully.

To ensure objectivity, precision, and thoroughness, much of this monitoring is accomplished through instruments. Pyrometers and thermometers, for example, measure the heat of volcanic rocks (the temperature of the cone rises before an eruption) or of associated waters, as in a crater lake. As rocks adjacent to the vent heat up, they become less powerfully magnetic, as surface or aerial surveillance with a magnetometer will establish. In some cases, rising temperatures can also be detected through a series of aerial infrared photographs. Unfortunately, none of these methods predicts eruptions definitively.

The two most commonly used instruments (and, on the whole, the most reliable) are the seismometer and the tiltmeter. The seismometer measures and records vibrations within the earth. When strong enough to be detected by humans, these vibrations constitute earthquakes. It has been known for centuries that seismic activity often precedes volcanic eruptions. Since the invention of the seismometer in the latter nineteenth century, however, it has also been possible to detect fainter, more deep-seated vibrations, signaling the subterranean rise of molten lava within the volcanic vent. Typically, such vibrations become stronger and more frequent as the time of eruption nears. Seismometry, therefore, is one of the most useful observational techniques available to the volcanologist.

As molten lava rises within the vent of an existing volcano, the cone of that volcano subtly changes shape. Although the changes are generally too small to be obvious, they can be ascertained and verified using a tiltmeter. This instrument can be in any of several forms (a pendulum, for example) but most commonly depends upon the displacement of a liquid, as in a carpenter's level. Laser beams have been used to measure tilt with great precision. In addition, some tumescence takes place so rapidly and conspicuously (generally along a seacoast) that detection by the naked eye is possible. Subsidence usually follows in any case, regardless of whether there has actually been an eruption.

Actual volcanic eruptions can last either seconds or days; a period of activity, characterized by frequent eruptions, can continue for years. During all or part of the times involved, it may well not be possible to inspect the volcano closely. First at Vesuvius, then at Hawaii and elsewhere, a number of the most active (or the most dangerous) volcanoes have been monitored constantly, by instruments and by humans, at volcano observatories. During a very violent eruption, instruments, observers, and even the observatory itself may be lost. In any case, volcanologists have always relied upon whatever eyewitness data they could gather to supplement their understanding of a volcanic event. Any eruption is a contribution to history.

Although photography was invented in 1839, early techniques did not permit the recording of subjects in motion. Thus, no photographs of any eruption exist before 1872, when on April 26, memorable views of Vesuvius were obtained. The first eruption to be photographed in the Western Hemisphere was that of Izalco, El Salvador, in 1894. There were then striking images of nuées ardentes at Mount Pelée by Tempest Anderson and Alfred Lacroix in 1902. Anderson's Volcanic Studies in Many Lands (1903) became the first picture book of volcanic phenomena. Eruptions of Mount Lassen in 1914 and 1915 were the first within the continental United States to be photographed. B. F. Loomis's Pictorial History of the Lassen Volcano (1926) is perhaps the earliest example of its kind.

Even in more modern times, it is still possible for a major eruption to take place without being observed by humans; Katmai, 1912, is a well-known example. The only recourse then available to volcanologists is that of hypothetical reconstruction based upon the physical evidence. This evidence generally consists of changes in the volcano's cone, adjacent geological effects, and the type and pattern of its discharges insofar as they can be ascertained.

Significance

In the early days of geology, it was believed by some that volcanoes were only local phenomena, deriving their power from the ignition of coal beds. If so, then they were of little consequence in the history of Earth and hardly more than a curiosity within it. Since the latter eighteenth century, when this view was promulgated by Abraham G. Werner, scientists have come to realize how mistaken it is.

In his Theory of the Earth (1788), James Hutton first emphasized that Earth's internal heat was the fundamental driving force underlying its surface permutations. Volcanoes, for Hutton, were safety valves intended to prevent his heat-engine Earth from blowing up. Unlike certain predecessors, however, he did not emphasize their major constructive role in creating the surface. The first theorist to hold essentially modern views regarding volcanoes was George Julius Poulett Scrope in Considerations on Volcanoes (1825). As more volcanoes were studied, three facts strikingly emerged. First, volcanoes are not randomly placed on Earth but are instead grouped into narrow belts—one surrounding the Pacific, in particular. Second, volcanoes are of different types, differing in origin, appearance, and behavior. Third, eruptions are also of different types, though individual volcanoes often produce more than one type, even during the same eruptive episode. By the beginning of the twentieth century, therefore, the understanding of volcanism and its role in the history of the earth had become much more sophisticated.

Two of the most important twentieth-century discoveries about volcanoes were that they are even more numerous in ocean basins than they are on land and that those on land are almost always associated with established or incipient plate boundaries. With very few exceptions, continental volcanoes occur as a by-product of subduction, the process through which one tectonic plate slides underneath another and is melted. Many theorists believe that the earth is less thermal now than it was in the past—that its geological activity in this respect is slowing down. Others insist that the most powerful episodes of volcanicity with which humans are familiar have taken place in relatively recent geological times. However this debate resolves, scientists regard volcanoes as the most visible indicators of the earth's still-active interior processes.

Principal Terms

ash: rocky, unconsolidated ejecta of sand-grain size

eruption: volcanic activity of such force as to propel significant amounts of magmatic products over the rim of the crater

lava: molten rock (as opposed to ash) erupted by a volcano

nuée ardente: a sudden basal surge of incandescent, heavier-than-air gas

Although volcanic eruptions are a normal part of the earth's workings, they have always been regarded with awe because of their unpredictability and power. Only within the last two hundred years has scientific understanding of them been achieved. During that time, certain specific eruptions (and recurring activity of certain volcanoes) have been especially influential.

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