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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The beads of Mozambique Island.

Mozambique Island, on the northern coast of the African country of the same name, was the first place where Portuguese explorers, having rounded the Cape of Good Hope, encountered the trade networks of the Indian Ocean. At this time the island was ruled by a Muslim sheikh, with merchants using the island as a base from which to trade with the African interior or wider Indian Ocean needing his permission to do so, with all such merchants needing to be Muslims themselves. The island was quickly brought under Portuguese rule, with a Captain appointed to rule the island on behalf of the Portuguese Crown, and became a crucial stopover on the journey between Lisbon and Goa. While the Portuguese Captain in theory had control over all commerce occurring in the port, in practice many commodities were not regulated, and the island gained as a reputation as place where fortunes could be made with little interference from the Portuguese authorities.

During the Early Modern Era, beads were extensively used by European traders as a means of currency, being both a portable, high value item, and a desirable commodity which they could control the supply of. This certainly appears to have been the case on Mozambique Island, where large numbers of beads, many of them apparently derived from shipwrecks off the coast of the island, are today collected from the island's sandy beaches and made into necklaces, which are then sold to tourists.

In a paper published in the journal World Archaeology on 22 November 2024, Tânia Manuel Casimiro of História, Territórios e Comunidades at Nova University Lisbon, Yolanda Duarte of Archaeology at Eduardo Mondlane University, and Jéssica Iglésias, also of História, Territórios e Comunidades at Nova University Lisbon, present the results of an analysis of the origin of beads from Mozambique Island, and the implications of this for the history of the island.

Today, beads are collected by shovelling sand from the beaches into 25-50 kg bags and taking these to a flat, clean surface, where the sand can be sifted through for beads. No permit is needed for this activity, and no attention paid to the archaeological context of the beads by the collectors. However, some of the necklaces made by the bead-gatherers have been obtained by local people with an interest in the island's heritage, and it is from such collections that Casmiro et al. gained the beads used in their study.

Process for recovering the beads. Casmiro et al. (2024).

Casmiro et al. examined a sample of 12 166 beads, recording the material they were made from, as well as their style. Many of the glass beads were apparently Venetian, with Venice being a major manufacturing centre for beads used as colonial trade goods from the sixteenth century onwards, although Casmiro et al. note that many 'Venetian' beads were in fact made in other European cities in imitation of the Venetian style. However, such beads are clearly of European origin, easily distinguished from Indian beads (also very common around the Indian Ocean) which tend to be carved from a mineral such as carnelian or agate. Because of the way in which the beads were obtained, it was not possible to date them by context, although it was possible to build up a limited chronology for beads from the sixteenth to nineteenth century, with a few beads coming from outside this period.

Strings of beads sold to tourists on Mozambique Island. Casmiro et al. (2024).

The majority of the beads (10 626) were made of glass. Most of these were of a single colour, with examples of white, black, blue, green, yellow, orange, and red beads being found, along with some which combine a several colours. These glass beads also vary greatly in shape, with tubular, oblate, cylindrical, ellipsoidal, spherical, bicone, and barrel-shaped beads all present. After glass beads, the most common were stone beads,  followed by coral, shell, bone, ivory, and plastic.

A 'Venetian' glass chevron bead transformed into a pendant. Casmiro et al. (2024).

The most common glass beads (7789 examples) are seed beads, small spherical beads at most a few millimetres across, which have been manufactured in Europe since at least the fifteenth century. Another common type are Green Heart Beads (540 examples), cylindrical glass beads made up of layers of different glass, with the innermost being green, giving a shimmering, multi-hued effect, which were produced in Venice between the fifteenth and eighteenth centuries.

(Top) Glass Heart Beads. (Bottom) Seed beads. Casmiro et al. (2024).

Hudson's Bay Beads (235 examples), sometimes also known as White Heart Beads, or Cornaline d’Aleppo, were made in Venice between 1830 and the early 1900s. These again were cylindrical beads with multiple layers, this time having an inner layer of white or yellow glass.

Hudson's Bay Beads. Casmiro et al. (2024).

Chevron beads (11 examples) were elongate beads made by building up multiple layers of glass onto a central star-shaped moulded cane. These beads were invented in the late fifteenth century by craftswoman Marietta Barovier of Murano, and made at a number of glassworks in Murano and Venice, and probably elsewhere, although it is not generally possible to tell where an individual bead was made.

Chevron beads from Mozambique Island. Casmiro et al. (2024).

A-Speo beads (186 examples) were made by drawing out a thick glass straw, which was then chopped into short segments. These segments were then placed on a metal rod, and placed in a furnace to melt them into a rounded shape (the name 'a-speo' derives from the Italian phrase for 'to skewer'). This technique was probably invented in Venice or Murano, but was practiced in many areas of Europe. 

A-speo beads from Mozambique Island. Casmiro et al. (2024).

Skunk beads (14 examples), were made in Venice (and probably other European bead-making centres) in the eighteenth and nineteenth centuries, by adding small globules of glass to an a larger glass bead of a different colour, to give a speckled effect. These were most commonly black with added white speckles, hence the name 'skunk beads', but other colour patterns were also produced. 

Skunk beads from Mozambique Island. Casmiro et al. (2024).

Tubular beads (12 examples) were first made in Venice in the fifteenth century, but due to their ease of manufacture, continued to be made at centres across Europe for the next six centuries. Padre, or Pekin Glass, beads were made in Venetian and Czech workshops in the nineteenth century, in imitation of blue glass beads from China, themselves made as a cheaper substitute for jade beads.

(Top) Tubular beads and (bottom) Pekin Glass beads from Mozambique Island. Casmiro et al. (2024).

Millefiori beads are glass with complicated floral patterns, made since Roman times. They are manufactured by producing glass canes with a flower-shaped cross-section, which are then cut into thin slices, which are in turn incorporated within blown glass products, including beads. The name millefiori derives from the Italian for 'thousand flowers'.

Millefiori beads from Mozambique Island. Casmiro et al. (2024).

Eye beads (2 examples), which superficially resemble eyes, have been made around the Mediterranean Basin, the Middle East, and South Asia for thousands of years, often as a charm against the Evil Eye. The earliest forms were made of clay, but the manufacture of glass eye beads can be traced back to about 1500 BC.

'King' or 'Golo' beads (2 examples) were made in Europe in the nineteenth and twentieth centuries as a high value trade item for African markets. There were large, striped, biconed beads which came in a range of colours, though green beads with yellow, black, and red stripes were the most common.

Dog Teeth, or ruffled beads (two examples) were made in Venice in the late nineteenth and early twentieth centuries, mostly for trade with Nigeria. These are black beads with an irregular shape, and a 'ruffle' of white marks (or 'teeth') around their centre.

A single Nueva Cadiz bead was found on Mozambique Island. These were squared, tubular beads in a distinctive blue colour, made originally in Venice for trade with the Americas, but which were subsequently made in a number of other European cities. These beads are very common at sites on the Atlantic coast of Africa, but surprisingly rare at sites on the Indian Ocean.

The single Nueva Cadiz bead found on Mozambique Island. Casmiro et al. (2024).

Bohemian beads (1147 examples) were made in the modern Czech Republic, where they developed a range of distinct techniques of their own, notably pressed glass. These beads often have vertical and horizontal lines, circular incisions, coloured bands, phytomorphic and zoomorphic decorations.

Bohemian beads from Mozambique Island. Casmiro et al. (2024).

Russian blue beads (183 examples) were a distinctive type of Bohemian bead produced in the eighteenth centuries. These beads were multifaceted with six, seven, or eight sides, and typically a transparent blue, although amber, green, and clear examples are also known.

Russian blue beads from Mozambique Island. Casmiro et al. (2024).

Vaseline beads (1 example), sometimes also called uranium beads because of the uranium used to tint the glass green, were large faceted of shaped beads made in Bohemia in the late  nineteenth and early twentieth centuries.

Haj beads (5 examples) were made in Bohemian the early twentieth century for export to the city of Mecca, where they were sold to pilgrims, often becoming heirloom objects within their families. Two of the examples found on Mozambique Island had moon-and-star symbols, while the remaining three had the name of the Prophet Mohammed written upon them.

Dutch opalescent beads (9 examples), sometimes known as moon beads, were glass beads made to resemble pearls by adding ash to the glass, made in the Netherlands, Bohemia, Germany, and Venice, in the eighteenth and nineteenth century.

Dogon beads (187 examples) are large, chunky beads with a rough texture, which were produced in Amsterdam and possibly Germany in the seventeenth and eighteenth centuries, principally for trade with the Dogon people of southern Mali, but were also traded to other areas of Africa.

Dogon beads from Mozambique Island. Casmiro et al. (2024).

Prosser beads (9 examples), sometimes known as Kakamba Prosser Beads after a town in what is now the Republic of Congo where they were popular. These were made in the nineteenth century by a French craftsman called Jean-Félix Bapterosses, who modified a technique developed by the Prosser Brothers of London to cold-press glass and porcelain buttons, instead producing disk-shaped opalescent beads.

While the majority of the examined beads were glass, stone beads were also common, with 996 in the collection. The most abundant stone types are jet and carnelian, with agate and garnet beads also quite common. Stone beads have been manufactured around the world, which can make it difficult to determine the origin of individual beads, although most stone beads found around the Indian Ocean originate from India or Southeast Asia. This potentially makes these beads the oldest on Mozambique Island, with some examples likely to have reached the island before the first Europeans.

Stone beads from Mozambique Island. Casmiro et al. (2024).

Three beads from Mozambique Island were identified as being of Chinese origin, although details of these are not given. China began to export large volumes of beads in the early twentieth century, something it does to this day, and has produced beads from porcelain, wood, cinnabar, cloisonné, enamelled metal, stones, and glass, among other materials.

Filigree is a form of intricate metalwork consisting of tiny beads and twisted threads soldered together, made in the Islamic world largely between the fifteenth and seventeenth centuries. Fifty five silver elements from Mozambique Island are probably derived from filigree jewellery, most likely originating from Mauritania.

Beads derived from Animal materials such as shell, bone, ivory, and coral were also quite common (469 examples), although it is difficult to assess where these came from, as these materials are available, and have been worked, across much of the globe.

Plastic beads (8 examples) are clearly of twentieth century origin, since the first plastic (Bakalite) was invented by the Belgian-American chemist Leo Hendrick Baekelandin 1909. Plastic beads are cheap and easy to manufacture, and are produced in many countries. The low number of these on Mozambique Island suggests that they may never have been a commercial import, but may have been brought to the island by people wearing them, or possibly even have floated there on ocean currents.

Finally, five items were found in the collection that probably did not start out as beads, but which had been repurposed as such. These were a black glass button or pendant, two jet buttons, a rectangular piece of jet with three diagonal incisions of unknown origin, and what appeared to be the bottom half of a Frozen Charlotte doll (a type of rigid doll, typically made out of china, made between about 1850 and about 1920, mostly in Germany for the US market).

Casmiro et al.'s study revealed the presence of a wide range of beads, made from a variety of substances, on Mozambique Island. Despite this variety, about 90% of the beads were glass, and of European origin. Glass trade beads have been considered to be powerful symbols of European colonial influence, which seems to be particularly relevant on Mozambique Island, a vital trade hub within the Portuguese Empire. The beads of the same designs as those found on Mozambique Island have been found at other sites around the world, although overwhelmingly in colonial contexts.

Glass beads were, of course, made before the fifteenth century, and it can sometimes be hard to differentiate these from later beads, but none of the glass beads found on Mozambique Island appear likely to be this old. The stone, and animal-derived, beads found on the island may date to before the arrival of Europeans in the area, although such beads continue to be made until the present day, making it hard to be certain of their age. Mozambique Island is known to have been a trading hub before the arrival of the Portuguese, but it appears to have become much more important once integrated into the global Portuguese network.

Curiously, the high abundance of European beads on Mozambique Island is in contrast to the situation in South Africa, where European beads are unusual at archaeological sites, but beads from India quite common. It has been suggested that this South African preference for Indian beads may have been established before the arrival of European traders, and that with South African customers unwilling to switch, European traders may instead have imported beads from India to cater for this market.

Casmiro et al. also note that the beads once brought to Africa by Europeans to trade for commodities such as slaves, ivory, and gold, have now taken on a new role in places such as Mozambique Island, being traded back to European tourists as a means of gaining hard currency, a much needed twenty first century trade commodity.

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Venice suffers the worst flooding in 53 years.

The city of Venice in northern Italy suffered its second worst flooding since records began on Tuesday 12 November 2019, with waters reaching 1.87 m above average levels at high tide, a level surpassed only by the flooding of 1966, when the waters reached 1.92 m above average. The flooding is thought tohave caused hundreds of millions of euros of damage to the historic city, as well as causing two fatalities. Both of the known deaths associated with the flood occured on the island of Pellestrina, which forms part of the barrier between the Venetial Lagoon and the Adriatic Sea; one of the fatalities was reportedly due to a man beong electricuted while trying to start a pump in his flooded house, the cause of the other has yet to be disclosed.

Flooding in St Marks Square, Venice, on Tuesday 12 November 2019. /AFP/Getty Images.

The flooding was caused by a combination of a spring tide, in which the Sun and Moon are aligned either on the same side of the Earth or directly oposite (as was the case this week), leading to high tidal waters, and a storm surge caused by a low pressure system over the Mediterranean. The low pressure above areas of sea causes water to rise there by ~1 cm for every millibar drop in pressure, leading to a storm surge that can overwhelm low-lying coastal areas.

 Animation showing how the alignment of the Sun and Moon causes higher 'spring' tides. NOAA.

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