Pagina's

The Moon and Earthquakes

We all known that the moon is responsible for the Earth's  tides, which are strongest when the sun and moon are aligned, during a full moon or a new moon. That same pull of the moon is also affecting the earths crust.
[Foto: Nicolette van Berkel]
For years, scientists have speculated whether the moon might play a role in earthquakes. It would make sense that the moon’s gravity could tug at a fault in the crust, especially one that is already close to failing and slipping. But nobody had demonstrated firm evidence for this.

Studying data from the past two decades, researchers measured the timing of high tides and reconstructed the amplitude of the moon’s pull at those times, focusing on the two weeks prior to large earthquakes[1]. They measured the amplitude of the tides against the timing of those quakes, and found some of the largest and most devastating earthquakes in recent memory happened when the Earth’s crust was under the highest tidal stress. They found that very large earthquakes, including the 2004 Indian Ocean (magnitude 9,3 with tsunami), 2010 Maule earthquake in Chile (magnitude 8.8) and the 2011 Tohoku-Oki earthquake in Japan (magnitude 9.1 with tsunami), tend to occur near the time of maximum tidal stress amplitude.

The mechanisms underlying this connection are not entirely clear. The moon’s pull causes tidal disruptions that are far lower than those experienced in an earthquake. And not every change in tide comes with an earthquake and not every earthquake comes with a change in tide. Part of the problem is that scientists still don’t know exactly what causes a major earthquake. But one theory is that they begin as smaller fractures that build up via a cascading process, where the moon is constantly pulling.

Research also found that both small and major earthquakes are not always triggered by the moon[2]. But some of them might be, and so we’d do well to pay closer attention to the subtle yet powerful ways in which the moon exerts its influence on our planet.

[1] Ide et al: Earthquake potential revealed by tidal influence on earthquake size–frequency statistics in Nature – 2016. See here.
[2] Van der Elst et al: Fortnightly modulation of San Andreas tremor and low-frequency earthquakes in PNAS - 2016

Fossilised tree helps date volcanic eruption 1,000 years ago

The ‘Millennium Eruption’ of Changbaishan (also known as Mount Paektu). The volcano is located on the border between China and North Korea. The eruption ranks among the largest medieval volcanic eruptions. It produced a widely-dispersed tephra layer. It was however unknown when this eruption precisely occured, with estimates spanning at least the tenth century CE.
Now, a team of scientists has analysed the partly fossilised remains of a tree killed by the eruption[1]. The tree was 264 years old when it was killed and buried by a flow of larva, hot ashand pumice. They knew that the tree must have been standing in 775 AD – a year that was marked by a burst of cosmic rays reaching the Earth – and this event was detected in the tree rings. Correlating ice core data made it certain that the eruption occurred in the last two or three months of 946 AD.

This secure date rules out the possibility that the 'Millennium Eruption' contributed to the collapse of the Bohai Kingdom (Manchuria/Korea) in 926 AD, as has previously been hypothesised. Further, despite the magnitude of the eruption, the data did not show a consequent cooling signal in tree-ring-based reconstructions of Northern Hemisphere summer temperatures.

Lead author, Clive Oppenheimer says: "The Millennium eruption has fascinated scientists and historians for decades because of its size, potential worldwide impacts, and the mystery surrounding when it actually happened. Lacking a clear historical record of the event, there have been dozens of attempts to date the eruption using conventional tree ring techniques. We got lucky thanks to the burst of cosmic radiation that bathed the Earth in the year 775. It was only recently recognised that this left a worldwide signature in trees alive at the time. Now we have a secure date for the eruption at last, we can be more confident in investigating the effects it has on the climate, environment and society."
The new date focuses attention on a chronicle from a temple in Japan that reports "white ash falling like snow" on the 3rd November 946 AD. This site is not near any of Japan's active volcanoes, and is close to where ash from the Millennium eruption has recently been identified in lake sediments. It may well pinpoint the actual date of the eruption since it would only have taken the ash clouds a day or so to reach Japan.

Changbaishan is a site revered by the Koreans. It is steeped in folklore and Koreans see it as their spiritual and ancestral home. Its eruption in 946 AD was one of the most violent of the last two thousand years and is thought to have discharged around 100 cubic kilometers of ash and pumice into the atmosphere - enough to bury the entire UK knee deep.

[1] Oppenheimer et al: Multi-proxy dating the ‘Millennium Eruption’ of Changbaishan to late 946 CE in Quaternary Science Reviews – 2017

[Review] Classical Traditions in Science Fiction

'Classical Traditions in Science Fiction' (edited by Brett M. Rogers and Benjamin Eldon Stevens) is a book that contains 14 essays by scholars of the classics, Greek, English, and philosophy. The essays explore connections between Jules Verne and the Greek satirist Lucian; Dune and the Iliad; Alien Resurrection and the Odyssey; antiquity and Western identity in Battlestar Galactica; the Iliad and Dan Simmons’ Ilium; The Hunger Games and the Roman Empire; and the graphic novel Pax Romana, which explores the transition from antiquity to a Christian world.

The term 'science fiction' is inherently vague and finding an all encompassing definition proves surprisingly elusive. Adam Roberts’ dictum that science fiction is 'premised on a material, instrumental version of the cosmos,' in contrast to its close ally, fantasy, which concerns 'magic, the supernatural, the spiritual.' Alternately, Susan Sontag summed up the whole genre as consisting of the 'imagination of disaster,' a fascination with dread of irresistible destruction.

At first science fiction did keep itself busy with 'novel ideas' about a possible future as dictated by Adam Roberts. Yet, the next wave of SF consisted of visions of a drab and depressing future as summed up by Susan Sontag. During the Victorian era, the world was changing fast, for some too fast. When extrapolated, the rapid industralisation with its smog and crumbling institutions, could herald an apocalypse in the future.

To be literature, one school of thought goes, a science fiction novel must be depressing, ginging an account of hubris and failure, such as George Orwell’s 1984. Some consider Mary Shelley’s Frankenstein the first science fiction: the optimism that drives scientific advance is thwarted by that unreliable factor, the human element.

Jesse Weiner’s essay “Lucretius, Lucian, and Mary Shelley’s Frankenstein” gives a thorough account of the book’s debate with the ancients, its later influence, and Shelley’s ambivalence about scientific progress.

But Frankenstein is subtitled The Modern Prometheus. Shelley drew upon the myth of Prometheus, who steals fire from the gods and is condemned to eternal damnation. Dr. Frankenstein is seeking higher human knowledge, the secret to the spark of life, and pays dearly for it.

'Classical Traditions in Science Fiction' is a book that contains a fascinating collection of essays that gives readers a new understanding of the place of science fiction within the Western literary tradition. Science fiction certainly harks its history back to classical Greek literature. Well worth your time. 

Largest impact crater near Falklands Islands?

Some 66 million years ago a comet struck the earth near Yucatan in modern day Mexico. The impact was so devastating that it heralded the end of the dinosaur. Evidence of that impact is the 200-kilometer diameter Chicxulub impact crater discovered in and near the Yucatan in the late 1970s.

But the earth has witnessed many more mass extinctions, the largest of them being the Permian–Triassic (P–Tr) extinction event, which occurred about 252 million years ago. It formed the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras. This mass extinction killed 90% to 96% of all species.

So, the question is: where is that impact crater?

A very large 250 to 300 kilometers wide circular geophysical anomaly (visible both in gravity and magnetic maps) is has been discovered on the Falkland Plateau to the northwest of West Falkland Island in the southern Atlantic Ocean[1][2].
The scientists point to specific features that indicate the basin is an impact crater. They note that it is completely buried by sediments from more recent eras, which indicates it was formed long before its surroundings, and that it has no topographic expression on the present sea floor. Key to the basin’s identification as a potential impact crater are the decrease in the strength of Earth’s gravity over the site, indicating a large basin filled with younger low-density sediments and a strong increase in the strength of Earth’s magnetism at the site. The latter is characteristic of large impact structures, such as the Chicxulub impact crater discovered in the Yucatan.

If the Falklands basin is really an impact crater, and it has some of the most telling features, then it is one of the largest known. The scientists estimate the age of the basin to be from the late Paleozoic Era–approximately 270 to 250 million years ago.

[1] Rocca, Presser: A possible new very large impact crater in Malvina Islands in Historia Natural – 2015
[2] Rocca et al: Geophysical evidence for a large impact structure on the Falkland (Malvinas) Plateau in Terra Nova - 2017

Mount Etna had glaciers during last Ice Age

The Mediterranean mountains were repeatedly glaciated during the last Ice Age which ended around 11,500 years ago[1]. Glaciers were present in most of the major mountainous areas from Morocco in the west to the Black Sea coast of Turkey in the east.

Some mountains supported extensive ice caps and ice fields with valley glaciers tens of kilometers long. Other massifs sustained only small-scale ice masses, although this was the exception rather than the norm. Glaciers still exist today and there is evidence that small glaciers were a common sight in many regions during the Little Ice Age.
The Mediterranean mountains are important for palaeoclimate research because of their position in the mid-latitudes and sensitivity to changes in the climate regimes of adjacent areas including the North Atlantic. These mountains are also important areas of biodiversity and long-term biological change through the Quaternary ice age.

Mount Etna (3329 meters) on Sicily is by far the highest mountain on the Mediterranean islands and one of the highest mountains in the entire region, yet clear evidence of glaciation has been buried by lava flows or obliterated by explosive volcanic activity, perhaps most recently in the Late glacial[2].
[U-shaped valley on the slope of Mt. Etna]

However, this volcano would have certainly been glaciated[3][4]. Researchers estimated a Pleistocene snowline of circa 2500 meter and other scientists have identified morphological evidence of a glacial valley on the northeastern flank of mount Etna[5]. They think it is reasonable to hypothesize that, during the Quaternary glaciation, a portion of the volcanic edifice could have been covered by thick ice sheets that excavated U-shaped valleys along their pathway. They have found this kind of evidence only in a small valley located in this area, that the scientists interpret to be of glacial origin.

[1] Hughes, Woodward (eds): Quaternary Glaciation in the Mediterranean Mountains – 2017
[2] Albert et al: Late glacial explosive activity on Mount Etna: Implications for proximal–distal tephra correlations and the synchronisation of Mediterranean archives in Journal of Volcanology and Geothermal Research - 2013
[3] Neri et al: Incidenza dei ghiaccia pleistocenici nell’evoluzione morfo-strutturale del Vulcano Etna (Sicilia, Italia) in Terra Glacialis - 2002
[4] Neri et al: Ghiacciai pleistocenici dell’Etna: un problema aperto in Istituto Lombardo, Accademia di Scienze e Lettere (Rendiconti Scienze) - 1994
[5] Carveni et al: First finding of glacial morphology on Mt. Etna volcano north-eastern flank (Sicily) in Geoitalia - 2007

When did humans first alter the global climate?

Palaeoclimatologist Professor William Ruddiman has been working on a hypothesis that posits that pre-industrial age humans raised greenhouse gas levels in the atmosphere. Looking back seven thousand years into the Holocene - the current 11,500-year-old geological epoch - Ruddiman has proposed that early agriculture emitted enough methane and carbon dioxide to offset what would have been a global cold cycle[1].
He began his thinking about early agriculture and greenhouse gases in the late 1990s when new data from Greenland and Antarctic ice cores was made public. Examining the data, Ruddiman was puzzled by the rise of atmospheric methane around 3000 BC.

In the glacial cycles of the past four hundred thousand years, this natural methane emissions rate is linked with the earth’s approximate 22,000 years precession cycle, the orbital cycle in which the earth shifts its axis of orbit. When the northern hemisphere summer is closest to the sun via precession, the highest amount of global methane is emitted. In the current interglacial precessional cycle, the methane maximum occurred eleven thousand years ago, at which there was the expected 700 parts per billion (ppb) methane concentration in the atmosphere—expected because comparable interglacial periods have that methane level.
However, at around five thousand years ago, Ruddiman noted that instead of continuing downward to a 450 ppb level, the methane leveled off at 560 ppb, and, reversing course, rose to around 660 ppb by one thousand years ago. Ruddiman correlated the methane trajectory reversal with rice paddy agriculture in Asia, which intensified roughly around the same time, five thousand years ago. After harvesting, the rice paddy areas emit methane in a similar manner to that of natural wetlands’ organic decomposition.

Ruddiman says that in contrast to the familiar view that human-caused greenhouse gases began with the industrial revolution, “the baseline of human effects on climate started earlier and that the total effect is larger.”

He is arguing that the significant footprint of human add-on to climate began thousands of years ago and not just 150 years or so, which is still the conventional view[2]. Even today climate scientists are not in total agreement as to whether early agriculture had a significant impact on global climate. Nonetheless, support for Ruddiman’s hypothesis has broadened in recent years [3].

Ruddiman: How Did Humans First Alter Global Climate? in Scientific American – 2005
Ruddiman et al: Does Pre-industrial Warming Double the Anthropogenic Total? in Anthropocene Review -2014
Ruddiman et al: Late Holocene climate: Natural or anthropogenic? in Reviews of Geophysics – 2016

Famine in Switzerland during 1816 and 1817

The aftermath of the 1815 eruption of Mount Tambora caused widespread famine during 1816 and 1817. Studies often look at rising mortality rates and declining birth rates to measure famine. While it is an indirect indicator, it does convey a sense of the intensity of the hardship[1]. Switzerland has been the subject of several studies on the subject.
A decreasing number of baptisms in Switzerland showed the severity of the crisis. During famines, a scissor-like demographic change could be observed in the rising mortality rate and decreasing number of baptisms. Over a long-term perspective, annual birth rates do not fluctuate as strongly as annual mortality rates, and researchers therefore regard birth rates as the more reliable indicator. A cohort census from the year of 1860 enabled the reconstruction of the development of the cohort at a district level in the entire nation.

Vulnerability in the famine years proved to be dynamic rather than static: in the first year of the crisis, the climate-sensitive wine-growing regions by the large lakes of the Swiss Plateau, the cities, and the canton of Bern were particularly vulnerable. In the second year, the crisis moved to eastern Switzerland and the valleys of the Jura, where the jewelry and watchmaking industry had expanded. Statistically seen, while only sufficient food was lacking in western Switzerland, a true famine prevailed in eastern Switzerland.

Single communities lost around one ninth of their population, not even counting emigration. It was very likely “the worst demographic crisis since the pest of 1629”[2].
The famine also affected the development of the average body height. The body is very sensitive to crises during its growth phase, since the uptake of nutrients was still very dependent on the economic conditions during the beginning of the 19th century. The average body height of persons born between 1800 and 1809 decreased significantly in parts of Switzerland. They suffered from both the previous Napoleonic Wars (1803-1815) as well as the famine (1816-1817).

Surprisingly, the average body height of the middle class decreased more than that of the lower class. It is possible that they were less likely to request help in overcoming the crisis than members of the lower classes, due to a fear of social stigmas. A similar scenario occurred in Swiss cities a good hundred years later during the First World War[3].

The crisis of 1817 had considerable demographic effects. On the one hand, the mortality rate increased, on the other hand the birth rate decreased. Some communities lost up to one ninth of their population.

[1] Krämer: Menschen grasten nun mit dem Vieh: Die letzte grosse Hungerkrise der Schweiz 1816/17 – 2015
[2] Schürmann: Bevölkerung, Wirtschaft, und Gesellschaft in Appenzell Innerrhoden im 18. und frühen 19. Jahrhundert. Appenzell – 1974
[3] Staub: Der vermessene menschliche Körper als Spiegel der Ernährungs- und Gesundheitsverhältnisse am Ende des Ersten Weltkrieges - 2016

Tambora and 'Darkness'

Tambora, on the island of Sumbawa, Indonesia—then the Dutch East Indies—began its week-long eruption on April 5, 1815. Volcanic ash circulated in the upper atmosphere for years after the event, blocking out sunlight and lowering averages surface temperatures globally and 1816 became known as the 'Year without Summer'.
In 1816, there was snow in New England in July and dark rain clouds swept over Europe throughout the summer months. Hungary reported brown snowfall, tainted by volcanic ash. With the cold came crop failures and famine. Food shortages compounded those already in place in the wake of the Napoleonic wars after retreating armies had helped themselves to whole harvests Leo Tolstoy in 'War and Peace' (1869), offers an vivid image of “... a splendid field of oats in which a camp had been pitched and which was being mown down by the soldiers, evidently for fodder.”.

But these bleak circumstances hit hardest in and around the Alpine regions of France, Germany, Austria, and Switzerland.

In April 1816, Mary Shelley traveled to Geneva, accompanied by her half sister, Claire Clairmont and her lover, Percy Shelley. Claire was eager to rekindle a romance with another British literary exile, Lord Byron.
The perpetual gloominess of what should have been summer skies inspired Byron to compose his miserable poem “Darkness,” in which the sun is permanently extinguished, and mankind dies:
I had a dream, which was not all a dream.
The bright sun was extinguish'd, and the stars
Did wander darkling in the eternal space,
Rayless, and pathless, and the icy earth
Swung blind and blackening in the moonless air;
Morn came and went and came, and brought no day,

During that same sunless summer Byron wrote another grim poem, “Prisoner of Chillon”. It delivered the same depressing feeling:
First came the loss of light, and air,
And then of darkness too:
...
For all was blank, and bleak, and grey;
It was not night it was not day;

Volcanism in Ethiopia speeded early human evolution

The Ethiopian Rift Valley hosts the longest record of human co-existence with volcanoes on Earth. Dramatic and rapid changes from volcanic activity in Ethiopia appear to have set the stage for the emergence of Homo sapiens around 200,000 years ago. According to new research, the first known fossil evidence for our species was unearthed there, where explosive volcanic activity was dramatically changing the landscape and environment[1].
"Pyroclastic flows -- hot currents of gas, ash and rock -- would have inundated large tracts of the rift floor while ash and pumice fallout from larger plumes are likely to have covered regions to at least 100 kilometers from the vent," commented lead author William Hutchison of the University of Oxford's Department of Earth Sciences.

The earliest humanoid fossils date to 195,000 years ago, so early humans likely witnessed the eruptions. Hutchison said that the volcanic eruptions occurred along the entire East African Rift System, which is a still-active continental rift where Africa is slowly being pulled apart. One segment runs through Ethiopia. Hutchison and his team reconstructed the eruptive history of a 124-mile-long segment of the rift in Ethiopia by studying the Aluto and Corbetti volcanoes. The researchers tried to determine the dates of erupted rocks. They also analyzed the sizes of eruptions along the rift over time.
"We suggest that an increased flux of melt from the mantle into the crust generated the large magma chambers that over-pressured and erupted 320,000–170,000 years ago," Hutchison said. "These events are called flare-ups."

“Major volcanic eruptions and the environmental devastation that followed might have greatly reduced hominid populations living in the rift zone," Hutchison said. "The eruptions themselves would have made certain sections of the rift uninhabitable, potentially for many thousands of years. These mechanisms provide a means of reducing and isolating certain populations which might have promoted human adaptation and evolution at this time."

"This suggests," he added, "that our earliest ancestors not only had to deal with changing climate but also with the environmental devastation caused by major explosive eruptions."

Earlier research supports that the region was already heavily populated with hominins long before our species emerged on the scene. Lucy (Australopithecus afarensis) was the only potential human ancestor species that roamed in what is now the Afar region of Ethiopia.

[1] Hutchison et al: A pulse of mid-Pleistocene rift volcanism in Ethiopia at the dawn of modern humans in Nature Communications – 2016

New fault discovered in southern California near the San Andreas

A new faultline has been discovered that runs parallel to the San Andreas. Located near the shallow, inland Salton Sea and to the west of the San Andreas fault, the new fault has been dubbed the Salton Trough Fault.

The evidence of the new fault was reported in a study and the study’s first author, Valerie Sahakian, said that discovering faults is part of being ready for earthquakes[1].
The scientists said that there haven’t been any earthquakes on record associated with the newly-discovered fault yet, and in fact, it might even be helping to absorb strain from the San Andreas. The earthquake-prone region could be due for an earthquake, as the southern San Andreas hasn’t had a major rupture in about 300 years.

Research has revealed that the region has experienced magnitude-7 earthquakes roughly every 175 to 200 years for the last 1,000 years. But it's been about 320 years since the last major earthquake. Based on the deformation patterns, this new fault might have accommodated some of the strain from the larger San Andreas system, so without having a record of past earthquakes from this new fault, it’s really difficult to determine whether this fault interacts with the southern San Andreas Fault at depth or in time.

In the Salton Sea area there has been a recent 'swarm' of little earthquakes— almost 200 of them. However, that swarm is unconnected to the new fault. Probably.

Sahakian et al: Geophysical Evidence for a San Andreas Subparallel Transtensional Fault along the Northeastern Shore of the Salton Sea in Bulletin Seismological Society of America – 2016

Swarm of earthquakes might awaken San Andreas Fault

In June 2016, I asked myself here if the San Andreas Fault was possibly ready to rumble. Now, just a few months later in October 2016, people are wondering if the San Andreas Fault is set to wake up in any moment. Following more than 200 earthquakes in a single day, officials in California issued an earthquake alert for residents of Southern California, prompting anxiety among many of the Californian residents.
According to Los Angeles Times, the swarm of earthquakes, which began rumbling under the Salton Sea and rupturing near Bombay Beach, gained concern among seismologists and officials because the tremors occurred at the tail end of the mighty San Andreas fault,

One can describe the San Andreas Fault as the sliding boundary between the Pacific Plate and the North American Plate. The series of quakes might have added stress to the San Andreas Fault which has not ruptured since 1680, making it way overdue for a significant earthquake.
Experts believe that if San Andreas Fault wakes up it might herald a 7.8 magnitude earthquake and the results will be nothing less than catastrophic.

How can small quakes trigger the awakening of the San Andreas Fault? Tiny earthquakes amplify the overall earthquake frequency on a given fault. In this case, it's the dreaded San Andreas Fault.

San Andreas Fault is ready to rumble

The San Andreas Fault is one of California's most dangerous fault lines. While the last big earthquake to strike the southern San Andreas was in 1857, the next 'big one' is long overdue.

The San Andreas system have been wound very, very tight. And the southern San Andreas Fault, in particular, looks like it’s locked, loaded and ready to go.

Other sections of the San Andreas Fault also are far overdue for a big quake. Further southeast of the Cajon Pass, such as in San Bernardino County, the fault has not moved substantially since an earthquake in 1812, and further southeast toward the Salton Sea, it has been relatively quiet since about 1680 to 1690.
The largest recorded earthquake in California was the 1857 Fort Tejon earthquake, with an estimated magnitude of 7.9. This earthquake ruptured the San Andreas Fault from Parkfield to Wrightwood, a distance of 350 km. The most destructive earthquake to date was the 7.8 magnitude 1906 San Francisco earthquake, when more than 3,000 people perished in the earthquake and the fires that followed.
Scientists have observed that based on the movement of tectonic plates, with the Pacific plate moving northwest of the North American plate, earthquakes should be relieving about 16 feet of accumulated plate movement every 100 years. Yet, the San Andreas Fault has not relieved stress that has been building up for more than a century. When the tension that has been building along the San Andreas Fault finally is relieved, it could potentially produce a magnitude 8 earthquake.

Already in 2008, the U.S. Geological Survey concluded that 'just' a magnitude 7.8 earthquake along the southern San Andreas Fault would cause more than 1,800 deaths, 50,000 injuries and $200 billion in damage.

You can keep a watchful eye on the earthquakes in Los Angeles here. Some other locations are potentially very unsafe to be living in too. See here or here.

Africa's Deadly Lakes

Let us start with a definition: a limnic eruption is a rare event in which dissolved carbon dioxide (CO2) suddenly erupts from deep lake waters, forming a cloud of exsolved gas that can suffocate wildlife, livestock and humans. Scientists believe earthquakes or volcanic activity can trigger for such phenomenon.
To date, this phenomenon has been observed only twice. The first was in 1984 at Lake Monoun (Cameroon), causing the asphyxiation and death of 37 people living nearby[1]. The event was associated with a landslide from the eastern crater rim, which slumped into deep water. A second, decidedly deadlier eruption happened in 1986 at neighbouring Lake Nyos, a deep lake high on the flank of an inactive volcano. This time the eruption released over 80 million cubic meters of CO2 and killing around 1,746 people and 3,500 livestock, again by asphyxiation[2].

While data indicate a volcanic source of the carbon dioxide, the gas is probably gradually build-up and not able to rise to the surface because of thermal layers in the water. The carbon dioxide is hovering near saturation and an earthquake or volcanic activity may suddenly alter the status quo. The thermal layers of cold and warmer waters are disturbed and the dissolved carbon dioxide is released.

Lake Monoun and Lake Nyos are relatively small lakes but other much larger density-stratified equatorial lakes might potentially harbour much more danger. Lake Kivu in east Africa, has a methane and carbon dioxide gas content that is higher by two to four orders of magnitude than that of the Cameroon lakes.
 
A gas burst from Lake Kivu in Rwanda - with two million people living nearby - would form a carbon dioxide and methane cloud up to 340 cubic kilometers in volume and expansion of the exsolving gas from deep water to atmospheric pressure would correspond to an energy release equivalent to 8 megatons of explosive[3]. Which is quite a large explosion.

[1] Sigurdsson et al: Origin of the lethal gas burst from Lake Monoun, Cameroun in Journal of Volcanology and Geothermal Research – 1987
[2] Kling et al: The 1986 Lake Nyos Gas Disaster in Cameroon, West Africa in Science – 1987
[3] Sigurdsson: Gas bursts from Cameroon crater lakes: a new natural hazard in Disasters - 1988

The eruption of Laki (1783)

Laki or more correct Lakagígar (Craters of Laki) is a volcanic fissure in the south of Iceland. On 8 June 1783, a fissure with 130 craters opened with earthquakes and explosions when groundwater interacted with the rising basalt magma. The eight-month emission of sulfuric aerosols resulted in one of the most dramatic climatic and societal events in historic times[1].

The eruption produced huge amounts of basalt and tephra. Gases were climbing to altitudes of about 15 km. These gasses, including millions of tons of hydrogen fluoride and sulfur dioxide, gave rise to what has since become known as the 'Laki haze' across Europe.
For two years following the initial explosions, Europe, North America and north Africa experienced bizarre weather phenomena. Within days, the haze produced by ash and smoke from Laki turned the sun blood red across Iceland. By June 10, ash was falling in Norway that withered tree leaves and grass in Bergen on the southwestern coast. That same day, in Denmark black ash discolored the sails and decks of ships as they approached the harbor.

Meanwhile, the haze – also referred to as 'dry fog' – spread swiftly across Europe. It arrived in Prague on June 16. On the 17th, the sun turned blood red in Berlin and on June 18, the haze appeared in Lyon, France:

“The fog was cold and humid, with the wind coming from the south and one could with eye look at the sun with a telescope without a blackened lens. The fog was such as the oldest men here have not seen before…”

That same day the haze covered Padua, Italy. Clearly, it was quite different from the ordinary fog the locals were used to. They wrote that it smelled of sulfur and that it withered the grass. In England, on June 23, a clergyman in Hampshire noted that the vegetation was yellow and looked “as if scorched with frost.” All of this makes it clear that the fog carried with it sulfur dioxide from Laki’s eruption.

By the end of June, the haze covered virtually all of Europe. In St. Petersburg, people recorded the dry fog on June 26. By June 30, it had reached Moscow. In central Asia, visitors reported unseasonable frosts throughout the summer as the haze kept the sun from warming the earth.
North Africans were also taking notice of the odd “cloud.” By the end of June it arrived in Tripoli, then in Syria. By July, the haze extended into Baghdad and the Altai Mountains.

In Egypt, it was noticed that the summer of 1783 was radically different from most summers in Egypt. Every spring the Nile River flooded, leaving behind wet, fertile soil in which the Egyptians grew their crops. However, that year the inundation was not sufficient. With no flood, the crops failed, with drastic consequences for the Egyptians.

The bizarre weather patterns triggered by Laki’s explosion meant that the monsoon that year was abnormally weak. In turn, this led to a severe droughts in India and Egypt. As a result of that drought, the Nile didn’t flood.

Egypt, so distant from Iceland, suffered the largest number of deaths in the wake of Laki’s eruption. Historians estimate that the population of Egypt was reduced by one sixth in the resulting famine.

The effects of the eruption lingered across North America and Europe as well. Parish records in England show a large increase in the number of deaths in July and August of 1783, presumably from respiratory illnesses caused by the haze.

In North America, the winter following the eruption was extremely cold and very long. The harbour in Charleston, North Carolina froze so hard that men and women could skate across it. In February 1784, ice floated down the Mississippi River to New Orleans and out into the Gulf of Mexico where it lingered, not melting.

In Iceland, a disease that caused the skin and flesh to rot off the living animals as they grazed in the fields. The symptoms were those of chronic fluorosis: the grazing livestock were poisoned because they ate vegetation that had been contaminated with fluorine as a result of the volcanic fallout.

Within days, the animals most severely affected were dead. Within a few months over 60% of all livestock in Iceland died, leaving the Icelanders to face the winter of 1783-84 without a proper food supply. The ongoing eruption, the colder than usual summer and the fallout of ash and poisonous haze meant that few if any crops could be saved. As a result, between 1783 and 1786 approximately 20% of the population of Iceland died of starvation and disease. This period is known in Icelandic as moðuharðindin, the 'Mist Hardships'.

[1] Thordarson and Self: Atmospheric and environmental effects of the 1783–1784 Laki eruption: A review and reassessment in Journal of Geophysical Research - 2003

Trap (in Vulcanism and Geology)

The term 'trap' has been used in geology since 1785–95 for rock formations that consist of multiple layers of solidified flood basalt that has eroded to a distinct stairstep-like landscape.

It is derived from the Swedisch and Norwegian word trappa ('stair') and refers to the step-like hills that form the landscape.

Trap rock, sometimes known as trapp, is any dark-colored, fine-grained, non-granitic intrusive or extrusive igneous rock. Types of trap rock include basalt, peridotite, diabase and gabbro. Trap is also used to refer to flood (plateau) basalts, such as the Deccan Traps and Siberian Traps. Both were massive eruptions have been linked to mass extinctions[1]. These eruptions were the result of a single mushroom-like mantle plume head that can generate a large igneous province within a few million years.
[Columbia River Basalts]

Other - much older - examples include the Karoo-Ferrar basalts/dolerites (South Africa and Antarctica), the Paraná and Etendeka traps (South America and Africa - formerly a single province separated by opening of the South Atlantic Ocean) and the Columbia River basalts (North America).

[1] Lin et al: Multiple volcanic episodes of flood basalts caused by thermochemical mantle plumes in Nature – 2005

Iceland's largest volcano hit by earthquakes

Iceland just raised the alarm after its largest volcano was hit by the biggest tremors since 1977. Katla – named after the word ketill ('kettle') after the shape of the volcano - is located in southern Iceland about 140 kilometers from its capital Reykjavik.
Two M4+ quakes rattled the crater of Katla on Monday, August 29, 2016. That was followed by a swarm of at least 10 more tremors at the volcano, which rises 1,450 meters into Iceland's chilly air. These are the largest temblors to occur to Katla since 1977.

The good news is that the Icelandic Meteorological Office is reporting that – so far at least - no tremor is currently recorded at Katla itself, which suggests that at least for the moment, no magma is making its way to the surface. Geologist Gunnar B. Guðmundsson said that while the tremors are quite large, there are as yet no signs that Katla is erupting. Scientists are however continuing to monitor the volcano.
Katla is one of Iceland’s more powerful volcanoes, and although it does not erupt very often on a human scale, geologically speaking it is considered very active. The volcano has erupted about 20 times since Iceland’s founding, although the last major eruption was in 1918. Historically, the feared Eyjafjallajokull has been known to erupt one to two years prior to Katla. Katla last erupted in 1955 and 1999. However, neither of those were large enough to break the ice covering its 10 kilometer-wide caldera. Its last major eruption was back in 1918, when it spewed ash for more than five weeks.

The lack of any harmonic tremor means that the likelihood of an imminent eruption is still low.

The Siberian Traps

About 65 million years ago a meteorite crashed into what is now the Mexican shoreline. The immediate result was the Chicxulub crater, the impact crater that is now buried beneath the Yucatán Peninsula in Mexico. The crater is more than 180 kilometers in diameter and 20 kilometers in depth. Scientists have calculated that the impacting rock was at least 10 kilometers in diameter.
It is now an accepted theory that the discovery of the Chicxulub crater lends support for the extinction of numerous animal and plant groups, including non-avian dinosaurs, may have resulted from a meteoric impact. In scientific circles this great dying is called the Cretaceous–Paleogene (K–Pg) extinction event, because its boundary clearly marks the end of Cretaceous Period and the beginning of Paleogene Period (K–Pg boundary).

Still, science isn't a religion and new theories and facts may add to our knowledge. Now new evidence is appearing that the extinction was not only the result of the impact of the meteor, but also of the also simultaneous eruption of the Deccan Traps in India[1].

But there were many more extinction events in the troubled history of our earth.
[Part of the Siberian Traps]

Around 250 million years ago, at the end of the Permian geologic period, there was another mass extinction so severe that it is the largest known species die-off in Earth's history. This time it wasn't a meteorite that created havoc, but a volcanic event of unimaginable scale[2]. For about a million years large floods of lava produced the Siberian Traps and covered over 2,000,000 square kilometers.
The continuous eruption of the Siberian Traps may have caused worldwide dust clouds and acid aerosols, which would have blocked out sunlight and thus disrupted photosynthesis both on land and in the ocean, causing food chains to collapse. The eruptions may also have caused acid rain when the aerosols washed out of the atmosphere. That may have killed plants on land. In the sea, shellfish would die because their calcium carbonate shells would simply have dissolved by the acid. More than 90 percent of marine species and more than 75 percent of terrestrial species disappeared from the face of the earth[3]. This is called the Permian–Triassic (P–Tr) extinction event, the Great Dying or the Great Permian Extinction.

[1] Petersen et al: End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change in Nature Communications - 2016
[2] Campbell et al: Synchronism of the Siberian Traps and the permian-triassic boundary in Science – 1992
[3] Burgess et al: High-precision geochronology confirms voluminous magmatism before, during, and after Earth's most severe extinction in Science Advances - 2015

A volcanic eruption in The Scream?

Large volcanic eruptions spew large amounts of dust and sulphuric acid into the atmosphere. These can result in a lowering of the global temperatures for some time and can lead to spectacular twilights. Fine ash tends to scatter shorter blue-violet wavelengths of light, and the remaining spectrum getting through is dominated by longer wavelength red to orange portions of the spectrum.

So, if you're a painter, would you be enticed to paint such a strange sky?

The explosion from the Krakatau volcano in 1883 was so strong that it unleashed a 40-meter high tsunami and turned the global skies red for months. But is it also responsible for The Scream, the famous painting by Edvard Munch?
Munch painted The Scream in 1893, ten years after the volcano erupted in Indonesia. However, research has suggested that he was actually depicting the explosion, which would have been visible to him even in faraway Norway[1].

On January 1892, he wrote a poem in his diary:
Jeg gik bortover veien med to venner – solen gik ned – Jeg følte som et pust av vemod – Himmelen ble plutselig blodig rød – Jeg stanset, lænede meg til gjerdet mat til døden – så ut over de flammende skyerne som blod og sværd over den blåsvarte fjord og by – Mine venner gik videre – jeg sto der skjælvende av angst – og følte et stort uendelig skrik gjennom naturen.

Translated:
I was walking along the road with two friends - the sun was setting - I felt a breath of melancholy - The sky suddenly became bloody red - I paused, leaned on the fence and feeling deadly tired – I saw over the fiery clouds like blood and swords over the blue-black fjord and the city - my friends were walking on - I stood there trembling with anxiety - and felt a huge endless scream through nature.

"The majority of those paintings reflect experiences that happened to Munch many years earlier," says Olson, lead researcher, "The death paintings are particularly clear. Death of the Mother and Death in the Sick Room, done in the 1890s, are based on the death of his mother in 1868 and the death of his sister in 1877. These experiences haunted him the rest of his life, as did the lurid, blood-red sky."

[1] Olsen et al: When the Sky Ran Red: The Story Behind The Scream in Sky & Telescope - 2003

Krakatau's effects in southern California

In 1884, the year after the eruption of Krakatau, summer temperatures in the northern hemisphere fell 1.2oC below average. Krakatau’s influence was seen and felt around the globe in vivid sunsets and stormy weather. Southern California experienced a year of record rainfall. Typical temperature and weather patterns did not recover for years. For the saguaro (Carnegiea gigantea), the perturbations appear to have been 'just right' for new growth.
A species of the arid southwestern United States, the saguaro is sturdy in maturity but delicate in the early years of its life. Though mature individuals can top 12 meters, new cacti grow only a few millimeters in the first year. Young saguaros are susceptible to heat and cold, vulnerable to drying out or freezing in the extremes of their desert environment. For a critical two to three years, until they grow large enough to withstand cold and drought, they demand cool summers, mild winters and sufficient rain: a combination of weather conditions abnormal for the Sonoran desert.

Research found that many of the large exemplars of the famous cacti in the Southwest today started their lives in the shadow of the 1883 eruption. Biogeographer Taly Drezner believes that distant volcanic eruptions and the emergence large numbers of saguaros are connected.
[Anak Krakatau - The Child of Krakatau]

“The saguaro is key to the survival of many species. Almost every animal in the Sonoran uses them in some way, as a nest site, or food, or a cool refuge,” said Drezner, a professor at York University in Ontario. Temperatures can easily exceed 40oC every day for weeks in summer, when saguaro seedlings have just germinated.

“I started noticing that these saguaro age cohorts followed notable volcanic eruptions,” said Drezner. “I knew that volcanoes drive milder summers and winters, and typically more rainfall for an extended period–two to three years after the event, which is a perfect window of time for the saguaro to get established and have a chance to survive.”

Saguaro boom years tracked the peaks in the dust index, particularly in the marginal environments. High volcanic dust levels also correlated with warmer, wetter, local winters and more rain in late spring.

On the origin of the name Krakatau

To this day the origin of the name Krakatau remains uncertain.

The earliest mention of Krakatau by name in the western world was on a 1602 map, created by Lucas Janszoon Waghenaer (ca. 1534 - 1606), who labelled the island 'Pulo Carcata' (pulo is the Sundanese word for 'island'). In the years that followed a series of variants of the name have been found, such as Crackatouw, Cracatoa, Rakata and Krakatao (in an older Portuguese-based spelling). The latter is the origin of the English version Krakatoa.
The first known appearance of the spelling Krakatau was by a Dutch docter Wouter Schouten in his travelogue, who passed by 'the high tree-covered island of Krakatau' in October 1658[1].

Linguist Van den Berg recites a story that the name Krakatau was the result of a linguistic error. According to a legend, an Indian price passed through the straits between Java and Sumatra. Observing the island, he enquired its name. The vessels master replied, ”Kaga tau" —a Jakartan and Betawinese slang phrase meaning "I don't know"[2].

[1] Winchester: Krakatoa: The Day the World Exploded – 2003
[2] Van den Berg: Vroegere berichten omtrent Krakatau. De uitbarsting van 1680 in Tijdschrift voor Indische Taal-, Land- en Volkenkunde – 1884

Was there ever a mega-eruption of Krakatau?

The 1883 eruption of Krakatoa in the Dutch East Indies (now Indonesia) began in the afternoon of August 26, 1883 and culminated with several destructive eruptions of the remaining caldera. On August 27, two-thirds of Krakatoa collapsed in a series of titanic explosions, destroying most of the island and its surrounding archipelago. The sound of the last explosion was the loudest in human history. It was heard more than 2000 kilometers away in the Andaman and Nicobar islands (“extraordinary sounds were heard, as of guns firing”); more than 3000 kilometers away in New Guinea and Western Australia (“a series of loud reports, resembling those of artillery in a north-westerly direction”); and even almost 5,000 kilometers miles away in the Indian Ocean island of Rodrigues, near Mauritius (“coming from the eastward, like the distant roar of heavy guns.”).
[Anak Krakatau]
So, the 1883 was a massive explosive eruption. At the moment the Krakatau is far from quiet and a new volcano is slowly rising from its remnants. Called Anak Krakatau ('Child of Krakatau'), it may become as large and violent as its mother.
[Anak Krakatau]
But there are rumours of an even larger event and the Javanese Book of Kings (Pustaka Raja) records that in the year 338 Saka (416 AD):

A thundering sound was heard from the mountain Batuwara [now called Pulosari, an extinct volcano in Bantam, the nearest to the Sunda Strait] which was answered by a similar noise from Kapi, lying westward of the modern Bantam. A great glowing fire, which reached the sky, came out of the last-named mountain; the whole world was greatly shaken and violent thundering, accompanied by heavy rain and storms took place, but not only did not this heavy rain extinguish the eruption of the fire of the mountain Kapi, but augmented the fire; the noise was fearful, at last the mountain Kapi with a tremendous roar burst into pieces and sank into the deepest of the earth. The water of the sea rose and inundated the land ... The water subsided but the land on which Kapi stood became sea, and Java and Sumatra were divided into two parts.

The myth claims that the islands of Java and Sumatra were once one and that the super-massive explosion divided them. While the myth names the volcano responsible for the destruction as Kapi, it is quite certain that Krakatau was the culprit.

But there is no geological evidence of a Krakatoa eruption of this size around that time. It may be that a mistaken date, which can be true because of the large time frame. The event can therefore refer to a later eruption in 535 AD, for which there is some corroborating historical evidence and may have been responsible for the global climate changes of 535-536 AD.

The Toba Catastrophe Theory

Around 74,000 years ago, the Earth witnessed a massive explosive eruption of Toba. It is speculated that the event resulted in a large-scale – but not global – volcanic winter during the next six to ten years. The resulting caldera still exists (100 by 30 kilometers) and is now filled with water.

The erupted mass was 100 times greater than that of the largest volcanic eruption in recent history, the 1815 eruption of Mount Tambora in Indonesia, which caused the 1816 'Year without Summer' in the Northern Hemisphere.
But the Eruption of Toba may have had an even greater effect. Our species, Homo sapiens, ventured out of Africa around 100,000 years ago, spread across Asia around 60,000 years ago and arrived on new continents and islands since then.

Hotly debated by scientists, the 'Toba catastrophe theory' claims that the Toba eruption is linked to a genetic bottleneck in human evolution about 50,000 years ago, which may have resulted from a severe reduction in the size of the total (world-wide) human population due to the effects of the eruption on the global climate. According to the genetic bottleneck theory, between 50,000 and 100,000 years ago, human populations sharply decreased to just 3,000–10,000 surviving individuals. The Toba eruption supposedly resulted in a near-global ecological disaster, including destruction of vegetation along with severe drought in the tropical rainforest belt and in monsoonal regions. For example, a 10-year volcanic winter triggered by the eruption could have largely destroyed the food sources of humans and caused a severe reduction in population sizes[1].
Well, because this is science (and not religion), people can dig up evidence to support or discredit it.

The eruption of Toba in 72,000 BC did produce voluminous ash deposits found across much of the Indian Ocean, Indian Peninsula, and South China Sea. A major climatic downturn was observed within the Greenland ice cores. But the eruption did not significantly impact the climate of East Africa and was therefore not the cause of a human genetic bottleneck at that time[2].

[1] Ambrose: Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans in Journal of Human Evolution – 1998
[2] Lane et al: Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka. in Proceedings of the National Academy of Sciences – 2013

Toba and its bipolar order

Toba is a volcano located in Indonesia on the island Sumatra. This massive volcano erupted some 74,000 years ago and left a crater that is about 50 kilometers wide. Expelled during the eruption was 2,500 cubic kilometers of lava. To put this into some perspective: this was 5,000 times larger than the Mount St. Helens eruption in 1980 in the United States. Toba's eruption was the largest on Earth in the last 2 million years.

We know that a somewhat 'smaller' (excusez le mot) eruption from Tamboro resulted in a measurable cooling of the climate for several years and 1816 is known as the 'Year without Summer'. So, what effect would Toba have had on the global climate and early humans?
The volcanic eruption threw huge clouds of ash and sulphuric acid into the atmosphere and up into the stratosphere, from where it spread across the entire globe in both the northern and southern hemispheres and fell down as acid rain. The ash has now been found in the ice of both the Arctic as well as the Antarctic[1].

“We have found the same series of acid layers from Toba in the Greenland ice sheet and in the ice cap in Antarctica. We have counted the annual layers between acid peaks in ice cores from the two ice caps and it fits together," explains glaciologist Anders Svensson, Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen. "This means that we can compare the ice cores from Greenland and Antarctica with a annual accuracy and thus combine our knowledge of climate change in the northern and southern hemispheres," emphasizes Svensson.
There has been much speculation about how such a huge eruption affected the climate. The giant clouds of sulphur particles that are thrown up into the stratosphere form a blanket that shields the Earth from the sun's radiation and this causes the climate to cool. But how much and for how long? Modelling has shown that such an enormous eruption could cause a cooling of up to 10 degrees in the global temperature for decades.

"In the temperature curves from the ice cores we can see that there is no general global cooling as a result of the eruption. There is certainly a cooling and large fluctuations in temperature in the northern hemisphere, but it becomes warmer in the southern hemisphere, so the global cooling has been short," explains Svensson.

But the eruption may still have had major consequences for nature, the environment and humans in large areas of Asia, where a clear layer of ash from the eruption has been found.

[1] Svensson et al: Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 kyr BP) in Climate of the Past Discussions - 2012

Tambora and its pyroclastic flows

The eruption of volcanoes present multiple dangerous phenomena: lava, tsunamis, sulphuric acids. The effect of lava is mostly local, but tsunamis can travel across oceans and create havoc on distant coasts. The sulphuric acid can have an long-lasting effect on global weather patterns. A volcanic eruption may also be accompanied by another deadly symptom: a pyroclastic flow.

During the 79 AD eruption of Mount Vesuvius, the Roman cities of Pompeii and Herculaneum were covered by super-heated ashes that are part of volcanic pyroclastic flows. Pyroclastic flows consist of a fluidized mix of hot lava blocks, pumice, ash and expanding volcanic gasses. These flows race down volcanic slopes at very high speeds. Pyroclastic flows behave like fluids and move at phenomenal speeds, often at over 150 kilometers an hour. This deadly mixture moves so fast that it can even travel over long stretches open water.
The 1815 eruption of Tambora was the largest eruption in recorded history. About 175 cubic kilometers of ash were erupted. Ash fell as far as 1,300 km from the volcano. In central Java and Kalimantan, 900 km from the eruption, one centimeter of ash fell. The eruption column reached a height of about 44 km. The collapse of the eruption column produced numerous pyroclastic flows, destroying everything in their paths and boiling and hissing into the sea 25 miles away. Huge floating rafts of pumice trapped ships at harbor[1].
The pyroclastic flows extinguished the tiny kingdom of Tambora. After 20 years of research, the first remnants of a Tamboran village were discovered under a layer of ash three meters thick and has unearthed the first clues about its culture[2].

“There’s potential that Tambora could be the Pompeii of the East, and it could be of great cultural interest,” said lead-explorer Sigurdsson, who believes the village includes a large wooden palace that he hopes to find on future expeditions. “All the people, their houses and culture are still encapsulated there as they were in 1815.”

[1] Self et al: Volcanological study of the great Tambora eruption of 1815 in Geology - 2011
[1] University of Rhode Island: URI volcanologist discovers lost kingdom of Tambora: Indonesian civilization was wiped out by largest volcanic eruption in history – 2006. See here.

Rinjani: The volcano that started the Little Ice Age

We all know that huge volcanic eruptions can have a considerable effect on the climate. The 1883 eruption of Krakatau in 1883 resulted in a fall of average global temperatures by as much as 1.2 degrees Celsius in the year following the eruption[1]. Weather patterns continued to be chaotic for years and temperatures did not return to normal until 1888. In comparison to this, the eruption of Tambora in 1815 was of an even greater magnitude and resulted in the 'year without summer' because of the effect on North American and European weather. Crops failed and livestock died in much of the Northern Hemisphere, resulting in the worst famine of the 19th century.

Now we turn to Gunung Rinjani, a still very much active volcano on the Indonesian island of Lombok. On the top of the volcano is a 6 by 8.5 kilometer caldera, which is partially filled by a crater lake that is locally known as Anak Laut ('Child of the Sea') due its azure colour. Located in the lake is the ominously growing crater cone called Gunung Barujari (Finger Mountain). That crater within a crater grew during a spate of activity from 1994 to 1995. On 31 October 2015, Mount Rinjani started erupting again.
So, what happens if such a massive volcano erupts in earnest?

Rinjani's huge caldera is probably formed sometime in the 13th century. Based on radiocarbon dates on charcoal, tephra dispersal and historical records, the eruption can be dated to 'between May and October of 1257'[2]. This colossal eruption is now considered the likely source of high concentrations of sulfur found in widely dispersed ice core samples and may have been 'the most powerful volcanic blast since humans learned to write'. There is even a preserved manuscript, Babad Lombok, written in Old Javanese on palm leaves, which records a catastrophic eruption of Rinjani. The massive eruption may have triggered a prolonged episode of global cooling and failed harvests, called the ‘Little Ice Age’, a cold snap defined variously within the 14th–19th century range.

Estimates based on sulfate deposition suggest that it yielded the largest volcanic sulfur release to the stratosphere of the past 7,000 years. The eruption triggered worldwide atmospheric and climatic effects of this eruption. Scientists argue that the source of this long-sought eruption is the Samalas volcano, once a twin peak adjacent to the Rinjani volcano, but destroyed during the explosion.
[A 'minor' eruption in 1994]
According to the new study, the Little Ice Age began abruptly between 1275 and 1300 A.D., triggered by repeated, explosive volcanism and sustained by a self-perpetuating sea ice-ocean feedback in the North Atlantic Ocean[3].

PS: The 'minor' eruption in the second image has its origin in Gunung Barujari, the 'small' volcano in the center of the massive caldera/lake of Gunung Rinjani you see in the first image.

[Update August 11, 2016] An eruption at Rinjani on 1 August generated an ash plume that rose to an altitude of 9.8 kilometers. Lombok International Airport temporarily closed as a result of that ash plume. Later, the situation returned to 'normal' although the public should stay at least 1.5 km away from the volcano. 
[1] Gleckler et al: Volcanoes and climate: Krakatoa's signature persists in the ocean in Nature - 2006
[2] Lavigne et al: Source of the great A.D. 1257 mystery eruption unveiled, Samalas volcano, Rinjani Volcanic Complex, Indonesia in Proceedings of the National Academy of Sciences of the United States of America. – 2013. See here.
[2] Miller et al: Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks in Geophysical Letters – 2012

Kos: Part of a Stratovolcano

Nowadays, the island of Kos is dominantly tranquil non-volcanic (and a popular tourist destination). However, around 66,000 years ago a large caldera was formed which deposited the widespread Kos Plateau Tuff, which blankets much of the western half of Kos and originated from a stratovolcano between Kos and Nisyros islands. The exact dimensions of the caldera are still uncertain, but may extend as much as 35 km from the southern coast of the island of Kos to the nearby Nisyros (therefore, largely submerged). Remnants of the pre-eruption stratovolcano are preserved on the islets of Pachia and Pyrgousa and as submarine volcanic rocks on Nisyros.
Kos was constructed with three cone-building stages. The whole scenery was related to the mythical Polybotes, a giant who fought Poseidon in their war against the gods. He was pursued by the god across the sea and crushed beneath the rock of Nisyros which formed the tip of the island of Kos. The numerous earthquakes which shake the island are ascribed to his writhing and his moaning. His name is derived from the Greek noun polybôtos, meaning 'fertile', or more literally 'feeding-many'.

Dating of four volcanic samples (material of eruption ejecta), from the island of Yiali near the Nisyros volcano has revealed, according to the scientists who conducted the measurements, a volcanic eruption which occurred during the second millennium BC (circa 1460 BC)[1]. This eruption could be a ‘rival’ for the environmental disasters correlated to this period. Usually these disasters are blamed on the eruption of Santonini/Thera that resulted in the demise of the Minoan civilization of ancient Greece.
But the volcano has displayed renewed activity. The present geodynamic activity encompasses high seismic unrest, widespread fumarolic activity, and numerous hot springs close to the sea level all around the island. Violent earthquakes and steam blasts accompanied the most recent hydrothermal eruptions in 1871-1873 and 1887.
These seismic events may be generated by magma ascent through the crust opening fissures and plains through magma injection, volume changes of the magma during emplacement and cooling, as well as magma degassing accompanied by immediate volume expansion of the gas[2].

After some intense seismic activity in 1996, a GPS network was installed in June 1997 and re-occupied annually up to 2002. Uplift between 14 to 140 mm was measured at all GPS stations[3].

Which might mean that a large eruption is in the making.

[1] Liritzis et al: A significant Aegean volcanic eruption during the second millennium B.C. revealed by thermoluminescence dating in Geoarchaeology - 1996 
[2] Sakkas et al: Surface Displacement Model of Nisyros Volcanic Field deduced from DlnSAR Analysis & DGPS Measurements in Bulletin of the Geological Society of Greece – 2003
[3] Lagios et al: Ground deformation of Nisyros Volcano (Greece) for the period 1995–2002 in Bulletin of Volcanology – 2005

Tambora and Cholera

The floods, droughts, starvation and disease in the three years following the eruption of Tambora in 1815 stem from the volcano’s effects on weather systems

Tambora’s huge explosive eruption not only led to the 'Year without Summer' but also had a little known effect on the disease ecology of the Bay of Bengal. The enormous cloud of sulfate gases ejected into the atmosphere by Tambora slowed the development of the Indian monsoon, the world’s largest weather system, for the following two years. Severe drought was the result.
Drought brought on by the eruption devastated crop yields across the Indian sub-continent, but more disastrously gave rise to a new and deadly strain of cholera. Cholera had always been endemic to Bengal, but the bizarre weather of 1816-17 triggered by Tambora’s eruption – first drought, then late, unseasonal flooding – altered the microbial ecology of the Bay of Bengal[1].

The cholera bacterium, which has an unusually adaptive genetic structure highly sensitive to changes in its aquatic environment, mutated into a new strain.This met with no resistance among the local population, and it spread across Asia and eventually around the globe. In 1817, cholera began spreading outside the Ganges delta. By September 1817, the disease had reached Calcutta on the Bay of Bengal and quickly spread to the rest of the subcontinent. By 1818 the disease broke out in Bombay, on the west coast. By century’s end, the death toll from Bengal cholera epidemic stood in the tens of millions.
Cholera is an infection of the small intestine by some strains of the bacterium Vibrio cholerae. So virulent is the bacterium that it can kill within hours. Even today, it is estimated that there are 1.4 to 4.3 million cases and 28,000 to 142,000 deaths worldwide due to cholera every year[2].

[1] Boucher et al: The out-of-the-delta hypothesis: Dense human populations in low-lying river deltas served as agents for the evolution of a deadly pathogen in Frontiers in Microbiology - 2015
[2] Lopez et al: The global burden of cholera in Bulletin World Health Organization - 2012