Did an unknown volcanic eruption create the conditions for the Black Death to enter medieval Europe?

Between 1347 and 1353, the Black Death spread across Europe, killing up to 60% of the population, leading to long-lasting demographic, economic, political, cultural, and religious changes which changed the continent, and eventually the world, beyond recognition. Recent palaeogenetic studies have now confirmed the long held belief that the pandemic was caused by the Plague Bacterium, Yersinia pestis, a zoonotic disease with wild reserves in a number of Rodent species. Despite the presence of a wild reserve, outbreaks of Yersinia pestis in Human and Domestic Animal populations are quite rare, with only three documented pandemics of the disease. The first of these, the Plague of Justinian, began around 541 AD, and persisted into the eighth century. The second, the Black Death, began around 1338 in Central Asia, and persisted in places into the early nineteenth century. The third began in China in the 1770s, and spread around the world; arguably this third Plague pandemic is still ongoing, with all wild reserves and outbreaks outside Asia apparently derived from this source.

Studies of the archaeological, historical and ancient genomic records have suggested that the Black Death was a genetically distinct strain of the Yersinia pestis Bacterium which probably originated in arid foothills of the Tien Shan mountains west of Lake Issyk-Kul in modern-day Kyrgyzstan. This spread along the trade routes of Central Asia, entering Europe via the northern Black Sea region in the 1340s. Notably, the Black Death abruptly entered Venice and other Mediterranean ports in 1347, presumably through the importation of infected Fleas from the Black Sea reason. 

From this time, there were repeated outbreaks of Plague across Europe until the early nineteenth century, although it is unclear if these represent a series of re-introductions, or the presence of a wild-reserve within Europe. Nor is it entirely clear why the Plague appeared in multiple Mediterranean ports at the same time, having been established in the Black Sea region for some time prior to this, without previously making the jump, though it has been suggested by several people that some socio-economic challenge led to a change in Human behaviour at this time, giving the disease an opportunity to spread.

In a paper published in the journal Communications Earth & Environment on 4 December 2025, Martin Bauch of the Department Humans and Environment at the Leibniz Institute for the History and Culture of Eastern Europe, and Ulf Büntgen of the Department of Geography at the  University of Cambridge, the Global Change Research Institute of the Czech Academy of Sciences, and the Department of Geography at Masaryk University, present evidence for a volcanic eruption at an unknown location in the years prior to the Black Death reaching the Mediterranean, which caused a regional famine, leading traders to seek new sources of grain, and thereby opening the region to the arrival of the Plague.

Bauche and Büntgen note that there has been extensive previous research into potential links between a volcanically induced climate crisis at the start of the  Late Antique Little Ice Age and the onset of the Plague of Justinian, but little previous investigation into such a link to the onset of the Black Death. They also note that ice cores from Greenland and Antarctica have revealed a spike in sulphur concentrations in 1345 considerably larger than the one caused by the Mount Pinatubo eruption of 1991, which probably represents an injection of about 14 megatons of sulphur into the atmosphere. Furthermore, there were also major spikes in 1329, 1336 and 1341, representing eruptions which would have injected roughly 3.7, 0.7, and 1.2 megatons of sulphur into the atmosphere, respectively.

Weather records from Japan, China, Germany, France, and Italy, all record the years from 1345 to 1349 as being exceptionally cloudy. A lunar eclipse in 1345 is recorded as having been exceptionally dark by witnesses in both Bohemia and China; something which can be another sign of a high volcanic dust level within the atmosphere. 

Studies of tree rings have shown that trees in the Spanish Pyrenees produced 'blue rings' in 1345 and 1346, which are interpreted as signs severe cold spells during the growing seasons affected growth. The production of blue rings in consecutive years is considered exceptionally rare. Studies of wood density across the Northern Hemisphere have suggested a progressive cooling from 1345 to 1347, with 1347 being the coolest year since 1257, when a cold spell was linked to an eruption on Mount Samalas on Lombok Island, Indonesia. 

May–September (MJJAS) temperature anomalies from 1119–2020 AD (uncertainties are expressed by grey shading), based on 534 maximum latewood density (MXD) measurement series from living and relict samples from Mountain Pine, Pinus uncinata, trees from undisturbed upper treeline ecotones in the Spanish central Pyrenees.  The pre-Black Death cold phase is indicated by the vertical blue shading. The right-side double-stained thin section shows two consecutive Blue Rings that were formed in 1345 and 1346 AD in a Mountain Pine, Pinus uncinata, from the upper treeline in the central Spanish Pyrenees. Bauche & Büntgen (2025).

While it is harder to assess rainfall in past than temperature, tree-ring data suggests that the cool period from 1345 to 1347 was accompanied by a prolonged west-east dipole in Europe, with wetter conditions around the eastern Mediterranean and dryer conditions around the western Mediterranean. Morocco, the British Isles, northern France, the Low Countries, Germany and southern Scandinavia, all appear to have suffered dry conditions, while the Iberian Peninsula, Italy, and the Balkans, had high spring and summer rainfall in those years.

Bauche and Büntgen also examined historical records from across Europe and beyond, which show a declining agricultural output from across Europe from 1345, and in particular a failure of (environmentally sensitive) Grape crops from northwestern Italy. Severe flooding was also recorded in Italy in the autumn of 1345 and the springs of 1346 and 1347, along with accompanying problems such as soil erosion. The winter of 1344/45 was exceptionally cold and snowy in the Middle East, with the winters of 1345/46 and 1347/48 being marked by drought and Locust invasions. 

Late medieval Italy had a highly urbanised population, with a complex grain supply system in place to support this population. Many city states, including major centres such as Bologna, Florence, Genoa, Siena, and Venice, had limited farmland and large urban populations, consequently importing grain over long distances to redress this imbalance. Only Rome and Milan were largely self-sufficient. Cities developed communal granaries run by officials with the power to manage these granaries, source supplies of grain from elsewhere, and prevent the export of grain from cities troubled by poor harvests or military conflicts. Typically, managing grain supplies was the second-largest source of expenditure for any late medieval Italian city-state, behind only military spending. Maritime powers such as Venice, Genoa, and Pisa, negotiated treaties with grain-producing areas such as Apulia, Sicily, Sardinia, North Africa,  the Aegean and the Black Sea region. 

In 1346/7 severe famines were recorded across parts of Spain, southern France, northern and central Italy, Egypt, and the Levant. This led to spikes in the price of grain in Spain, Italy, Egypt, and even the Arabian Peninsula. Strict grain regulations were implemented in many Italian cities from 1346, at least in part to grain-shortage induced civil unrest.

Northern Italy suffered a series of famines during this interval, which appear unrelated to any political crisis, supporting a climate-related problem as the cause. Initially, this shortfall was met by increased imports from southern Italy, but it quickly became clear that this would not be sufficient to alleviate the crisis, and that more imports would be needed from further afield. 

At this time, Venice and Genoa were in a state of conflict with the Mongols of the Golden Horde, who had been trying to eliminate Italian power in the Black Sea region. This had led to the Italian cities blockading the ports of the Black Sea, preventing the Mongols from trading with the Mediterranean. However, the onset of famine in Italy led to a re-appraisal of this situation, with a ceasefire and renegotiation of trading arrangements leading to a restoration of grain trading, saving Venice from starvation.

The Plague Bacterium, Yersinia pestis, had been present in the Black Sea region for some time, and it is likely that it would eventually have reached the Mediterranean at some point. However, Bauche and Büntgen contest that the lifting of the trade embargo against the Golden Horde in response to the volcanically-induced famine affecting northern Italy was the immediate cause of the Black Death reaching multiple Mediterranean ports in a short interval. 

The trade embargo was lifted in 1347, and shortly thereafter, Venetian and Genoan trading vessels began entering the trading ports of the northern Black Sea and the Sea of Azov, returning to Italy laden with grain. The Plague appeared in Venice less than two months after the first such trading vessel. In March 1348 Venice lifted an embargo on the export of grain to Padua, with the first Plague outbreak there coming shortly after. Records of the grain trade to Florence and Sienna are less clear, but again the first Plague outbreaks in these cities were associated with the abating of the famine. Notably, this first wave of Plague outbreaks did not affect cities such as Rome, Milan,Verona, Ferrara, Ravenna, and Bari, which controlled larger grain producing areas, and were not involved in grain imports from the Black Sea region. Elsewhere around the Mediterranean, Marseille, Palma de Mallorca, and many other important port cities had Plague outbreaks before the end of 1347, probably as a result of grain shipments from Genoa. Smaller cities such as Savona, Ventimiglia, and Tunis, began to suffer outbreaks in April 1348, again probably linked to Genoan grain shipments. The reached Trento along with grain shipments from Venice, and from their spread across the Alps into northern Europe. 

Grain trade and plague dispersal. Main aspects of the Venetian, Genoese, and Pisan grain trade network that prevented much of Italy from starvation in 1347 AD but also brought the Plague Bacterium, Yersinia pestis, to Venice and other Mediterranean harbours during the second half of 1347 AD, from where it spread rapidly. Location of the tree ring-based climate reconstructions is indicated (with two sites in Scandinavia not shown). Map is an equal-area, pseudo-cylindrical Mollweide projection with greyscale referring to elevations above sea level. Bauche & Büntgen (2025).

In 1344, a decade-long papal embargo on trade with the Mameluke Sultanate was lifted, enabling Italian merchants to resume trade with the Middle East. Following the resumption of trade with the Black Sea region, Venetian ships began carrying grain to Alexandria, and the ports of the Levant, while Mameluke traders began visiting the ports of the Crimea. While individual shipments are harder to trace for these ports than those of Italy, these ships are probably responsible for the arrival of the Black Death in North Africa and the Middle East.

Thus the resumption of trade with the Black Sea region appears to have resolved the immediate problem of a widespread famine, but also led to the simultaneous import of the Black Death to ports around the Mediterranean. The subsequent rapid spread and high fatality rate for the disease may also have been a result of a population weakened by famine. The sophisticated trade system developed by the Italian city states to ensure against famine appears to have made those states, and their allies around the Mediterranean and Europe, particularly vulnerable to the spread of the Plague. Bauche and Büntgen conclude that the Black was not just a singular event, but rather the culmination of a prolonged crisis which began with a climate crisis and then a famine.

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Magnitude 3.3 Earthquake on the north Lancashire coast.

The British Geological Survey recorded a Magnitude 3.3 Earthquake at a depth of 3 km, near Sliverdale in Lancashire, England, slightly before 11.25 pm GMT on Wednesday 3 December 2025. There are no reports of any damage or casualties associated with this event, and nor would any be expected of an Earthquake of this size, but it was felt across Lancashire, with isolated reports of people feeling movement as far away as Newcastle and Nottingham.

The approximate location of the 3 December 2025 Lancashire Earthquake. USGS.

Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone  to quakes than the rest of Wales or most of England. However, while quakes in southern England are less frequent, they are often larger than events in the north, as tectonic pressures tend to build up for longer periods of time between events, so that when they occur more pressure is released.

The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process.

(Top) Simplified diagram showing principle of glacial rebound. Wikipedia. (Bottom) Map showing the rate of glacial rebound in various parts of the UK. Note that some parts of England and Wales show negative values, these areas are being pushed down slightly by uplift in Scotland, as the entire landmass is quite rigid and acts a bit like a see-saw. Climate North East.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here. 

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Over 1000 people thought to have died in Indonesia, Malaysia, and Thailand as a result of Cyclone Senyar.

At least 1000 people are thought to have died, with more than 2700 more known to have been injured and more than 500 still missing after Cyclone Senyar swept across Sumatra and Peninsula Malaysia on 26-28 November 2025. The storm formed as a tropical depression in the Strait of Malacca on 22 November 2025, intensifying to become a tropical cyclone before making landfall on the northern part of Sumatra at about midnight on 26 November 2025. The storm moved southwards along the coast of North Sumatra, before sweeping back across the Strait of Malacca to make landfall on Peninsula Malaysia on 27 November. On 28 November the storm swept out over the South China Sea, where it dissipated several days later without making landfall again.

Flooding in Padangsidimpuan, North Sumatra on 26 November 2025. Badan Nasional Penanggulangan Bencana/Wikimedia Commons.

The passage of Cyclone Senyar resulted in at least 753 deaths on Sumatra, with a further 2600 injured and 526 people still missing, largely as a result of flooding and landslides. Over 1.2 million people on the island have been displaced because of the storm with about 3.3 million affected in some way, across the provinces of North Sumatra, West Sumatra, and Aceh. The storm is reported to have destroyed 3600 homes, and damaged a further 5800, along with 344 bridges and 324 schools.

A woman clearing mud from a house in the town of Meureudu in Aceh Province, Sumatra, following the passage of Cyclone Senyer. Hotli Simanjuntak/EPA.

The storm caused less damage in Peninsula Malaysia, where people had more time to prepare, with three fatalities, and 34 000 people evacuated from high-risk areas ahead of the storm. However, in neighbouring part of southern Thailand, flooding associated with the storm killed at least 267 people, with most of the fatalities occurring in Songkhla Province, according to government figures; although some sources have accused the government of downplaying the size of the disaster, with suggestions that more than 1000 people may have died in Songkhla Province alone. In addition, at least 102 people were injured, with two homes destroyed and 1074 damaged, along with 228 roads, 12 bridges, 41 schools and 38 temples. The city of Hat Yai in Sonhkla Province received 372 mm of rain on 21 November, more than is typical for the entire month of November, and more rain than has fallen on the city in a single day in 300 years of records.

Flooding in Songkhla Province, southern Thailand, on 26 November 2025. AP.

Tropical storms, called Cyclones in the Indian Ocean and South Pacific, are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

The formation of a tropical cyclone. Natural Disaster Management.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms. 

The formation and impact of a storm surge. eSchoolToday.

However, Cyclone Senyar is unusual in that it formed in a part of the world not usually prone to tropical storms; it is only the first such storm ever to form in the Strait of Malacca, and the second to cross these waters, after Typhoon Vamei, which formed in the South China Sea in 2001, and crossed Peninsula Malaysia from east to west. This is because the Strait of Malacca is close to the equator, an area where it was once thought that tropical storms could not form, as the Coriolis Force is not strong enough. However, warming global sea temperatures appear to be making this possible, as more heat is effectively more energy, and this is the fifth such near-equator storm of 2025. This means that communities in these areas are not as used to tropical storms as communities in areas where they are a long-standing problem, and infrastructure has not typically been built with large storms in mind, greatly increasing the damage and casualties caused when they appear.

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Ongoing Diphtheria Crisis affects eight African countries.

Between 1 January and 2 November 2025, 20 412 cases of suspected Diphtheria were recorded across the African continent, with 1252 people believed to have died from the disease (a case fatality ratio of 6%) according to a press release issued by the World Health Organization on 21 November 2025. Eight countries have recorded ongoing epidemics of Diphtheria, Algeria, Chad, Guinea, Mali, Mauritania, Niger, Nigeria, and South Africa. Epidemics in some places have been ongoing since 2023, with the disease continuing to spread to new areas. 

In many areas, laboratory confirmation of cases remain the exception rather than the rule, due to a shortage of suitable testing facilities, as well as a shortage of diagnostic equipment. There is also currently a global shortage of Diphtheria Antitoxin, the most effective treatment for the disease, as well as a shortage of suitable facilities for administering the treatment in many areas. Many of the countries affected have extremely fragile healthcare systems, combined with large numbers of displaced persons and in many cases ongoing civil conflicts, leading to a strong possibility of the disease spreading further within the region. This has led the World Health Orgnization to categorise the crisis as a Grade 2 Emergency under the terms of the Emergency Response Framework.

Diphtheria is a highly contagious vaccine-preventable disease caused mainly by the Actinomycete Bacterium Corynebacterium diphtheria but also by the related Corynebacterium ulcerans. It spreads between people mainly by direct contact or through the air via respiratory droplets. The disease can affect all age groups; however, unimmunized children are most at risk.

Symptoms often come on gradually, beginning with a sore throat and fever. In severe cases, the Bacteria produce a poison (toxin) that causes a thick grey or white patch at the back of throat. This can block the airways, making it hard to breathe or swallow, and also creates a barking cough. The neck may swell in part due to enlarged lymph nodes.

Treatment involves administering Diphtheria antitoxin as well as antibiotics. Vaccination against Diphtheria has been effective in reducing the mortality and morbidity from Diphtheria dramatically. Diphtheria is fatal in 5-10% of cases, with a higher mortality rate in young children. However, in settings with poor access to Diphtheria antitoxin, the case fatality ratio can be as high as 40%.

Niger is suffering an ongoing Diphtheria epidemic which began in the Zinder Region in November 2022, and which has subsequently spread to the Adadez and Diffa regions, with 34 of the country's 72 districts reporting cases. In 2025, there have been 1926 suspected cases, with 122 deaths (a case fatality ratio of 6.3%), with 765 cases confirmed by laboratory testing. Attempts to combat the outbreak have been hampered by a severe humanitarian crisis, driven by civil conflict, climatic effects, economic breakdown, and a large number of displaced persons, with around 2.6 million people currently reliant upon humanitarian assistance. A vaccination program was initiated in September 2025, with uptake reported to be good, and a second round is being planned.

A woman receives a dose of Diphtheria vaccine in Niger. World Health Organization.

Nigeria has been suffering an ongoing Diphtheria epidemic since December 2022, and has the highest number of cases in Africa. In 2025 till November 2, a total of 12 150 cases were reported (8587 of which have been confirmed by laboratory testing), with 884 deaths (a case fatality ratio of 7.2%). Diphtheria has been reported this year from 240 local government areas in 30 of Nigeria's 36 states. This outbreak is disproportionately affecting children and adolescents, and is being exasperated by a low vaccine take-up rate, with around 71% of the population having received a first dose of vaccine and about 67% having received all three recommended doses. Nigeria is suffering from a shortage of vaccines, a limited ability to carry out laboratory testing, a poor public understanding of Diphtheria, and weak infection control practices.  

A Diphtheria outbreak has been ongoing in Chad since mid 2024, with 4462 cases and 47 deaths reported in 2025 to 2 November, a case fatality ratio of 1.1%. Most of the cases have been among children aged 3-13 years. Chad is currently at the centre of a humanitarian crisis triggered by conflicts in multiple neighbouring countries, as well as political instability within its own borders. It is currently home to 1.4 million refugees, including 870 000 from Sudan, as well as about 300 000 internally displaced people. This makes it hard to assess the vaccination status of much of the population in areas where the outbreak is ongoing.

A patient receiving treatment for Diphtheria at a hospital in Chad. Seigneur Yves Wilikoesse/Medecins Sans Frontieres.

Mali is suffering an ongoing Diphtheria epidemic, which began in the northern part of the country in September 2024, with 430 suspected cases and 29 deaths (a case fatality ratio of 6.7%) in 2025 till 2 November. The epidemic spread significantly during 2025, reaching seven of the country's eleven regions and 30 of 75 districts, including the capital city, Bamako. Mali is currently suffering a complex humanitarian crisis, driven by civil conflict and climate-related disruptions, with 6.4 million people currently reliant on humanitarian assistance. Vaccine uptake is low, with 91% of the population having received a first dose, and only 82% all three recommended doses. The country also has a shortage of Diphtheria Antitoxin, as well as a healthcare system which has been severely overstretched by the multiple crises in the country.

Mauritania is suffering a Diphtheria outbreak which began in September 2024, and has spread to 11 of the country's 53 departments, with 849 suspected cases and 33 deaths (a case fatality ratio of 4%). Mauritania has a fairly high vaccination rate for Diphtheria, with 95% of the population having received a first dose of the vaccine, and 86% having received all three doses, but it is also currently home to a population of 118 000 Malian refugees, with vaccine records only available for about 10% of this population. The epidemic also coincides with an outbreak of Rift Valley Fever in the same areas. Efforts to combat these outbreaks has been hampered by poor funding, logistical problems, and a shortage of skilled healthcare workers.

A child receiving treatment for Diphtheria at the Mbaerra Refugee Camp in Mauritania. World Health Organization.

A Diphtheria outbreak began in Guinea in June 2025, with 476 suspected cases and 123 deaths (a case fatality ratio of 25.8%, currently the highest of any affected country). Four of the country's 38 prefectures have been affected, although the outbreak is centred on the gold mining areas of Kankan, particularly in Siguiri District. Only 70 cases have been laboratory confirmed, largely due to a lack of facilities. Guinea also has a low vaccine uptake, with only 77% of the country having had a first vaccine dose, and 63% having received all three recommended doses. The country also has a chronic shortage of Diphtheria Antitoxin, as well as few facilities for treating patients.

Algeria is generally considered to be Diphtheria-free, with a high vaccination rate (98% of the population having received at least one vaccine dose, and 92% having received the recommended three doses). However, in recent years the southern part of the country has become host to a large number of displaced people, fleeing conflict zones in the Sahel Region. In 2024 this area suffered a Diphtheria outbreak in which over 900 people were infected and 119 people died (a case fatality ratio of 13%). A new outbreak was reported in southern Algeria in October 2025, with 13 people infected and two deaths. 

Uniquely among affected countries, the Diphtheria epidemic in South Africa is unrelated to the ongoing crisis in the Sahel Region. The country has a long history of sporadic outbreaks, although these are usually small and quickly contained. The current outbreak, however, first appeared in Western Cape in October 2023, and quickly spread to KwaZulu-Natal, since when it has proven hard to contain. In 2025 till November 2, a total of 106 cases of Diphtheria have been reported in South Africa, all of them laboratory confirmed - a total which includes 37 asymptomatic carriers. The epidemic is still centred on Western Cape, but cases have also been reported in Limpopo, Gauteng, KwaZulu-Natal, and Mpumalanga. Vaccination cover remains low in South Africa, with 76% of the population having received a first dose and 74% all three doses, and this is believed to be worsening. South Africa is also affected by the global shortage of Diphtheria Antitoxin, as well as a health service stretched by multiple other issues.

Geographical distribution of Diphtheria outbreaks in Africa, January 2025 until 2 November 2025. World Health Organization.

Diphtheria is a recurrent problem in many areas of Africa, with 18 789 cases reported between 2020 and 2022. However, this has become much worse since 2023, with 57 000 cases and about 2000 fatalities reported in 2023 and 2024, across  Algeria, Chad, Gabon, Guinea, Mali, Mauritania, Niger, Nigeria and South Africa, with Guinea, Niger, and Nigeria being the worst affected. The disease particularly infects children under 15, and females more than males. About 50% of those infected in 2020-24 are thought to have been unvaccinated. 

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