Homo sapiens exhibit extreme behavioural plasticity, mediated by culture and technology, that permits us to adapt rapidly to new environments and situations. Understanding the role that past climate change played in selecting for Homo sapiens’ adaptability is a key question in human evolution research. The arid and semi-arid Kalahari Basin in southern Africa is an ideal region for addressing this question because fossil, genetic, and archaeological evidence supports an early origin for Homo sapiens in southern Africa. The growing archaeological record of the Kalahari Basin reveals that significant behavioural innovations accumulated in the region over the course of the Middle and Late Pleistocene, including ochre use, hafted hunting weapons, fishing, and figurative paintings. Here, we report the results of interdisciplinary investigations at two locales in the southern Kalahari; Ga-Mohana Hill and Witberg 1. The archaeological and palaeoenvironmental record (based on U-Th dating of tufas) at Ga-Mohana Hill reveals that site occupation correlated with a previous period of increased effective precipitation ~110-100 ka, and preliminary results suggest a more complicated relationship between occupation and precipitation after that time. At Witberg 1, Middle Stone Age archaeology is associated with the shoreline of a previously unidentified palaeolake. Current investigations are focused on dating the Witberg deposits, analysing the lithic technology, and generating palaeoenvironmental archives using phytoliths and diatoms. Collectively, this research provides a rare opportunity to evaluate Middle Stone Age occupation across a changing landscape from both stratified rockshelters and sealed open-air sites, to explore the complex interactions between past climate change and early human behaviors, and to better understand the origins of Homo sapiens extreme adaptability.

How to cite: Wilkins, J., Pickering, R., von der Meden, J., Gliganic, L., Brown, K. S., Esteban, I., Khumalo, W., Chiwara, P., Sahle, Y., Kirsten, K., and Schoville, B. J.: Investigating the impact of Pleistocene climate change on early humans in the southern Kalahari, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8123, https://doi.org/10.5194/egusphere-egu21-8123, 2021.

The late Quaternary saw the extinction of a great number of the world’s megafauna (those animals >44 kg), an event unprecedented in 65 million-years of mammalian evolution. Extinctions were notably severe in North America where 37 genera (~80%) of megafauna disappeared by around the late Pleistocene/Holocene boundary (~11.7 thousand-years-ago, or ka). Scholars have typically attributed these extinctions to overhunting by rapidly expanding human populations (i.e., overkill), climate change, or some combination of the two. Testing human- and climate-driven extinctions hypotheses in North America, however, has proven difficult given the apparent concurrency of human arrival in the Americas—more specifically, the emergence of Clovis culture (~13.2–12.9 ka)—and terminal Pleistocene climate changes such as the abrupt warming of the Bølling-Allerød interstadial (B-A; ~14.7–12.9 ka) or near-glacial conditions of the Younger-Dryas stadial (YD; 12.9–11.7 ka). Testing these hypotheses will, therefore, require the analysis of through-time relationships between climate change and megafauna and human population dynamics. To do so, many researchers have used summed probability density functions (SPDFs) as a proxy for through-time fluctuations in human and megafauna population sizes. SPDFs, however, conflate process variation with the chronological uncertainty inherent in radiocarbon dates. Recently, a new Bayesian regression technique was developed that overcomes this problem—Radiocarbon-dated Event-Count (REC) modelling. Using the largest available dataset of megafauna and human radiocarbon dates, we employed REC models to test whether declines in North American megafauna species could be best explained by climate change (temperature), increases in human population densities, or both. On the one hand, we reasoned that if human overhunting drove megafauna extinctions, there would be a negative correlation between human and megafauna population densities. On the other hand, if climate change drove megafauna extinctions, there would be a correlation between our temperature proxy (i.e., the North Greenland Ice Core Project [NGRIP] δ¹⁸O record) and megafauna population densities. We found no correlation between our human and megafauna population proxies and, therefore, no support for simple models of overkill. While our findings do not preclude humans from having had an impact—for example, by interrupting megafauna subpopulation connectivity or performing a coup de grâce on already impoverished megafauna—they do suggest that growing populations of “big-game” hunters were not the primary driving force behind megafauna extinctions. We did, however, consistently find a significant, positive correlation between temperature and megafauna population densities. Put simply, decreases in temperature correlated with declines in North American megafauna. The timing of megafauna population declines and extinctions suggest that the unique conditions of the YD—i.e., abrupt cooling, increased seasonality and CO₂, and major vegetation changes—played a key role in the North American megafauna extinction event.

How to cite: Stewart, M., Carleton, C., and Groucutt, H.: Climate change, not human population growth, correlates with late Quaternary megafauna declines in North America, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2844, https://doi.org/10.5194/egusphere-egu21-2844, 2021.

The purpose of this paper is to look at the prehistoric human settlement patterns in the northern Great Basin of the United States
in light of a variety of climate proxies.  The intent is to look at the response of Great Basin hunter-gatherers in response to extreme climatic events.  
Focus will be on two US Geological Survey designated hydrographic basins: the Black Rock Basin and 
the Truckee Basin.  The Black Rock Basin contains the Quinn River which originates in the Montanna Mountains and terminates into a seasonal lake
on the Black Rock playa.  The Truckee Basin contains the Truckee River which flows from Lake Tahoe in the Sierra Nevada range 
to the terminal Pyramid Lake.  

Radiocarbon dates from excavated archaeological sites in the two basins are used as a demographic and settlement proxy.  Climate proxies
from the two basins include: oxygen isotope data from Pyramid Lake, pollen cores from Mud Meadows spring and Summit Lake, and tree ring 
data from the Jackson Mountains. 

Both basins see initial human settlement during the Younger Dryas period, with a growth in population/settlements through 8000 BP. After
approximately 7800 BP, there is a paucity of dated sites until approximately 4000 BP.  Whether this is due to the 8.2 kya BP climatic event and/or
the Mount Mazama volcanic eruption, is uncertain.  Oxygen isotope data from Pyramid Lake does indicate a period of hyper-aridity throughout the
northern Great Basin between ca. 8-4 kya BP.  The aridity declines after 4 kya based on the oxygen isotope data, and settlement in the 
two basins increases.  With the onset of the Late Holocene Drought, ca. 2500 BP, population/settlement declines are seen except around 
major lakes, north of 42N latitude, and elevations above 2000m. After 2000 BP, population/settlement increases throughout both basins.  Notable
increases of population/settlement occurs in the Late Antique Little Ice Age and continues throughout the Medieval Climatic Anomaly (MCA). Environmental proxy data indicates the MCA was a period of extreme aridity in the northern Great Basin. Despite ameorilating conditions in both basins after the MCA and in the Little Ice Age, population/settlement declines after circa 700 BP.    

How to cite: Hall, M.: Climatic Extremes and Human Resilience: An Examination of Two Hydrographic Basins in the Great Basin (northern Nevada, USA), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13370, https://doi.org/10.5194/egusphere-egu21-13370, 2021.

The compact size of the semi-isolated Maltese archipelago and its relatively challenging environmental conditions, with limited soil cover and variable precipitation averaging around 600 mm a year, mean that the area offers an important case study of human-environment interactions. Following an initial phase of Neolithic settlement, the ‘Temple Period’ in Malta began from around 5.8 ka and within a few hundred years the spectacular ‘temples’ which characterize the period and are among the oldest buildings in the world began to be constructed. After over a thousand years this long-lived culture came to a seemingly abrupt end at ca. 4.4 to 4.2 ka, and was followed by Bronze Age societies with radically different material culture, funerary behaviour, and architecture. Various ideas concerning the reasons for the end of the Temple Period have been expressed. These range from climate change, to invasion, to social conflict resulting from the development of a powerful ‘priesthood’. Here, the idea that the end of the Temple Period was caused by aridity induced by the 4.2 ka event is tested. The 4.2 ka event is a classic example of an abrupt climate episode, and while it has been linked with several examples of significant societal change, such as the end of the Old Kingdom in Egypt, its details and relevance have been debated. To evaluate the Maltese example, archaeological data is fused with an understanding of the geology and palaeoenvironment of Malta, as well as consideration of the wider regional situation at this time in terms of demography and material culture, as well as the possible role of factors such as disease epidemics. The Maltese example forms a fascinating case study for understanding issues such as chronological uncertainty, disentangling cause and effect when several different processes are involved, and the role of abrupt environmental change in impacting human societies. Ultimately, it is suggested that the 4.2 ka event played a significant role in the end of the Temple Period, but this has to be understood within the specific geological and societal circumstances of the Maltese islands.

How to cite: Groucutt, H. S.: The 4.2 ka event and the end of the ‘Temple Period’ in Malta, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10760, https://doi.org/10.5194/egusphere-egu21-10760, 2021.

The Atlantic Forest is a major biogeographic zone of Brazil, encompassing biodiverse evergreen, semi‐deciduous, and Araucaria forests. It is presently home to millions of people, and, consequently, has experienced high levels of defaunation/deforestation through fragmentation and habitat loss in recent years. A growing archaeological and palaeoecological consensus indicates growing anthropic influences on forest distribution during the pre-Columbian period, hand-in-hand with land use intensification and increasing social complexity over time. 

Against this backdrop, this paper expands upon recent palaeodemographic work in South America to evaluate the role of long-term (centennial-scale) hydroclimatic oscillations (and the antiphasing thereof) in the Atlantic Forest domain as a potential "push factor" engendering human-driven forest expansion. It will synthesise archaeological, palaeoclimatological, and palaeoecological records, evaluate data quality, and identify areas for expansive future research. 

How to cite: Riris, P. and Gregorio de Souza, J.: Pre-Columbian palaeodemography in the Atlantic Forest (Brazil): evaluating the role and influence of extreme hydroclimatic oscillations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16059, https://doi.org/10.5194/egusphere-egu21-16059, 2021.

The impact of super volcanic eruptions (Volcanic Explosivity Index 7-8+) on human evolution is a topic that has invited much debate and controversy (Ambrose 1998, Petraglia et al. 2007, 2012; Clarkson et al., 2020), and has typically focused on the impacts on human populations within the last 100-200kya (e.g. Groucutt 2020). What is less well understood is whether there is any clear evidence to show how super-volcanic eruptions, and their subsequent impacts on paleo-environments and climates, may have influenced hominin evolution over the last c. 5mya. Previous studies using first and last hominin appearance dates have suggested that orbitally-induced climatic cycles (eccentricity, obliquity and precession) may play a role in hominin speciation events, but that only obliquity shows any significant relationship with extinction events (Grove 2012a). Firth and Cole (2015) subsequently suggested that selected super-eruptions may have acted as critical enhancers to particular orbital forcing events.

This paper revisits the Firth and Cole (2015) study and presents a comparison of super volcanic eruptions against first and last hominin appearance dates; orbitally induced climatic cycles; global temperature (measured using the LR04 Benthic Stack – Lisiecki and Raymo 2005); and broad technological behavioural changes in order to assess to what extent such eruptions may have impacted, either directly or indirectly, on human evolution at different temporal and geographic scales. Such large eruptive events certainly do seem to disrupt climatic conditions for significant periods of time at a generational level (Harris 2008). Where data is fine grained enough, volcanic activity also seems to impact on human population dispersals, through push and pull factors, and drive changes in the behavioural record (e.g. Groucutt 2020). However, at the broad evolutionary scale, volcanic eruptions do not seem to lead to a significant turnover of hominin species (at least in regard to the resolution of the data currently available). Therefore, we suggest that future work should seek to bring these two perspectives of scale together to better understand super volcanoes in terms of the complex interplay of changing local conditions and their impacts on the broader global picture of human evolution.

References:

Ambrose, S.H., 1998. Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans. Journal of Human Evolution. 34, 623–651.

Clarkson, C. et al. 2020. Human occupation of northern India spans the Toba super-eruption ~74,000 years ago. Nature Communications 11: 961.

Firth C.R. and Cole J. 2015: A review of super-volcano eruptions and their impact on hominin evolution. INQUA XIX Congress: Japan, July.

Groucutt, H. 2020. Volcanism and human prehistory in Arabia. Journal of Volcanology and Geothermal Research 402: 107003.

Harris, B. 2008. The potential impact of super-volcanic eruptions on the Earth’s atmosphere. Weather 63 (8): 221 – 225.

Petraglia, M.D., et al.,  2007. Middle Paleolithic assemblages from the Indian subcontinent before and after the Toba super-eruption. Science 317, 114–116.

Petraglia, M.D., Korisettar, R., Pal, J.N., 2012. The Toba volcanic super-eruption of 74,000 years ago: climate change, environments, and evolving humans. Quaternary International. 258, 1–4.

How to cite: Cole, J. and Hosfield, R.: Super-volcanic eruptions and impacts on hominin evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7563, https://doi.org/10.5194/egusphere-egu21-7563, 2021.

Near 12,850 cal. yr. BP, the Younger Dryas cooling (YD) abruptly reversed the warming trend from the last glacial to the present interglacial at high northern latitudes. Subsequent YD-onset-related changes, including hydroclimate shifts, affected ecosystems and human societies worldwide. The main YD trigger – e.g., a massive meltwater input into the North Atlantic Ocean, volcanic gas aerosols from the cataclysmic Laacher See (LS) eruption in the Volcanic Eifel, Germany, or an extraterrestrial body impact or airburst – remains widely debated and unclear. We have obtained lake sediment cores from three sites located in the Bohemian Forest Mts., Czechia-Germany-Austria border area (distance of 450–470 km from the LS volcanic crater). The characteristic LS tephra glass shards were documented in all three cores using X-ray fluorescence scanning, magnetic susceptibility measurements, and direct observation by scanning electron microscopy, and their concentrations were quantified by a TESCAN Integrated Mineral Analyzer (TIMA). Our geochemical results show the closest match with the so-called MLST-B phreatomagmatic phase of the LS eruption. Moreover, a significant amount of LS-(crypto)tephra-related phosphorus (up to 0.15%), often the limiting nutrient in both terrestrial and freshwater ecosystems, was found in the sediments. The discovery of the LS volcanic ash in the Bohemian Forest points to a wider distribution of this (crypto)tephra than has been known so far (evident transport also in the eastern direction). It opens up new potential for tephrochronologically supported research of Late-glacial sediments in eastern Central Europe and exploring the role of the event in human prehistory. In addition to the LS cryptotephra, we observed magnetically extracted iron-rich microspherules with signs of high-temperature melting and quenching in all studied sediment cores. Their maxima (3–36 objects per 1 g of dry sediment) were situated 2.2–3.1 cm above peaks in the LS tephra shard concentrations. Such exotic objects were reported from numerous sites on several continents where more impact-related proxies were documented by proponents of the YD impact hypothesis. Based on this evidence, we hypothesize that the Allerød-Younger Dryas transition in Central Europe was likely affected by more than one extreme event. The LS eruption was followed by an event during which the iron-rich microspherules were formed. The ongoing study is supported by the Czech Grant Foundation (20-08294S – PROGRESS).

How to cite: Vondrák, D., Kletetschka, G., Svecova, E., Hruba, J., Štorc, R., Hrstka, T., Heurich, M., van der Knaap, W. O., and Stuchlik, E.: Two extreme events near the Allerød-Younger Dryas transition: A story read from Bohemian Forest lake sediments (Central Europe), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13283, https://doi.org/10.5194/egusphere-egu21-13283, 2021.

Approximately 13ka BP, the Laacher See volcano (East Eifel volcanic field, Rhenish Shield) erupted cataclysmically¹. The details of this eruption as well as its impact on climate, environments and human in the near and far fields have been intensely researched offering rich data for designing Realistic Disaster Scenarios that consider, specifically, the potential consequences of renewed volcanic activity in the Eifel and, more generally, the consequences of similar extreme events/natural hazards on societies in Europe². In this paper, I review the available evidence relating to the Late Pleistocene eruption with particular focus on (i) new climate modelling³, (ii) the impacts of the tephra-fall on ecosystem services^4,5 and (iii) the disruption to contemporaneous forager migration and communication networks^6,7. Building on this, I reflect on how this evidence has recently fed into a special museum exhibition that places a Laacher See-type eruption in the year 2100 (https://www.moesgaardmuseum.dk/en/exhibitions/after-the-apocalypse/). Combing principles of evidence-based climate communication^8–10, Realistic Disaster Scenario thinking^11,12 and state-of-the-art exhibition design, the exhibition addresses likely impacts on economy, travel/communication networks, politics and culture within the context of Anthropocene warming as projected by the IPCC scenarios.

References:

How to cite: Riede, F.: Apocalypse then! Apocalypse now? Using the Laacher See eruption (13ka BP) for Realistic Disaster Scenario design, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14745, https://doi.org/10.5194/egusphere-egu21-14745, 2021.

Climate responses to major tropical volcanic eruptions bring about complex social effects with lasting historical consequences. Based on several historical episodes, we establish an argument that the weather-altering eruption of Samalas (1257), which shifted the Asian monsoon and caused global weather anomalies, may have played a significant role in the breakup of the Mongol Empire. The empire’s end came soon after the largest eruption of the Common Era, and its political situation devolved into open warfare between claimants to the throne. While this has previously been described in the historiography as a purely political series of events guided by individual actors’ motivations, the state’s collapse occurred in fact amidst a series of epidemics, droughts, famines, and erratic weather which can be plausibly tied to aftereffects of the eruption. 

Focusing on a few case studies, textual sources mention a fatal epidemic in southwestern China in 1259 which suddenly ended the life of Möngke Khan, the last ruler of the unified Mongol Empire. Based on terminology and descriptions of the epidemic, records of cholera across the larger region, and an ostensible relationship between other historical mega eruptions and ensuing pandemics, we argue that 1259 may have seen a cholera outbreak. Secondly, we note that the hydroclimatic aftereffect of extreme drought over Mongolia and Eastern China, peaking in 1259-60, weakened cavalry forces based in Inner Asia and the Mongolian Plateau. The drought and resultant famine had major historical consequences by influencing the outcome of the civil war (1259–1264) fought between Möngke Khan’s surviving brothers for control of the empire. Mongolia lost its undisputed central position as the state fragmented into at least six independent khanates, marking the end of the unified Mongol Empire. While political events and human decisions played major roles in developments, and societal responses could ameliorate the Samalas eruption’s impact, we argue that ignoring it leaves out an important element of our understanding of these events of global historical significance. The work of the researchers is presently being prepared for publication.

How to cite: Kern, Z., Pow, S., Pinke, Z., and Ferenczi, L.: Samalas and the Fall of the Mongol Empire:  A volcanic eruption’s influence on the dissolution of history’s largest contiguous empire, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3460, https://doi.org/10.5194/egusphere-egu21-3460, 2021.

Large volcanic eruptions that reach the stratosphere cool the surface climate and impact the atmospheric circulation, feeding back on the local climate. The mid-6^th century is an outstanding period in climate history that featured an extreme cold period, including one of the coldest decades in the past 2000 years. It was triggered by the 536/540 CE volcanic double event, creating the strongest decadal volcanic forcing in the last two millennia. During this period societal changes are recorded around the world, like the Great Migration period and the outbreak of the Justinian Plague. However, not a lot is known about the causal relationships between global cooling and societal change. Less is known also, about the impact of the large-scale atmospheric circulation on the regional climate, vegetation and society in Scandinavia after this volcanic double event. Here we aim to improve this understanding by combining global climate and regional growing-degree-day (GGD) modeling with climate proxies and archaeological records from Southeastern Norway.

We use PMIP4 past2k runs and the MPI-ESM ensemble simulation of the 6^th/7th century (520-680 CE), to analyze the atmospheric circulation, surface climate and vegetation changes as a response to the volcanic double event of 536/540 CE, over Scandinavia, specifically Southeastern Norway. Thereby we focus on the response of the major circulation patterns that influence the climate over Northern Europe: the positive and negative North Atlantic Oscillation, the Scandinavian blocking and the Atlantic ridge. The results of the GDD model, driven with the MPI-ESM model input, are compared to local pollen and climate records and archaeological data (e.g. grave density and settlement records) to shed more light on the local climate, vegetation and society impact. This comparison allows us to better understand how a natural hazard influenced local areas and climate records in Southeastern Norway. This study is part of the VIKINGS project, which focuses on the impact of volcanic eruptions on climate, environment and society in Norway/ Scandinavia.

How to cite: van Dijk, E., Gundersen, I. M., Bajard, M., Høeg, H., Løftsgård, K., Iversen, F., Timmreck, C., Jungclaus, J., and Krüger, K.: Large volcanic eruptions as a natural hazard: The impact of the 536/540 CE double event on the atmospheric circulation, surface climate, vegetation and society in Scandinavia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12270, https://doi.org/10.5194/egusphere-egu21-12270, 2021.

Around 8200 years ago, the Storegga tsunami, caused by a massive submarine landslide off the coast of Central Norway, struck the coasts of west Norway, Scotland and Doggerland. This event is well known from wide ranging geological and palaeobotanical work undertaken over the last 30 years. What has been less explored, however, is the potential social impact that this natural freak event had on the Mesolithic hunter-gatherer societies living on the coasts and shores of the North Sea. What happened in the tsunami’s aftermath? It has been widely assumed to have been a disaster – but was it? What constituted a disaster in the Mesolithic? In the Mesolithic, people were hunter-gatherer-fishers, they lived by, off, and with the sea. Settlement sites in West Norway were concentrated along the outer coast. People lived on the shores of islands and headlands, or along resource rich tidal currents. Eastern Scottish Mesolithic sites are also found on contemporary coasts, while the coasts of central Doggerland have long since become submerged. What happened to groups in these landscapes on the day the sea became a monster and in the years that followed? In this paper, we will outline a newly started project that will investigate the social impact of the tsunami in areas of the North Sea that have distinctive Mesolithic histories. These coastal inhabitants had, for millennia, developed their own traditions to engage with and learn how to exploit and keep safe from the sea. What can we learn about Mesolithic societies by investigating how communities handled the forces of a tsunami? Responses identified in the archaeological material and environmental archives can potentially inform us of social structures, institutions or ways of living that made the existing societies resilient or vulnerable.

How to cite: Nyland, A., Warren, G., and Walker, J.: When the sea become a monster? The social impact of the Storegga tsunami, 8200 BP, on the Mesolithic of northern Europe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2008, https://doi.org/10.5194/egusphere-egu21-2008, 2021.

Paleogeographic data give grounds to assert that at the end of the Valdai Ice Age, transgressions of the Caspian Sea took place, and the sea level during these periods exceeded the current one by tens of meters. The physical mechanisms, climatic or others, that could have caused such an extreme sea level rise have not yet been established. At the same time, in the modern Volga basin, traces of very large ancient river channels are widespread, which could have been formed by ancient rivers with the water flow 2-3 times larger than the modern rivers. Thus, the hypotheses of the extreme rise in the Caspian Sea level can be reduced to considering possible sources of the increase in the flow of the ancient rivers. However, the question of possible sources of such a significant river flow remains open. At the end of the Paleocene - beginning of the Holocene, precipitation over the Caspian Sea catchment was not higher than now, the contribution of melted glacial waters in the Late Glacial Era was also insignificant.  Hypotheses about significant changes in the catchment area of the Caspian Sea during those times are not confirmed by paleogeographic data either. In our work, we test the hypothesis that the river inflow into the ancient Caspian Sea could significantly exceed the current inflow due to the spread of post-glacial permafrost over the sea catchment area, which contributed to a decrease in runoff losses due to infiltration into frozen soils.

The physical validity of the above hypothesis was tested using numerical experiments with a hydrological model of the Volga River basin, developed on the basis of the ECOMAG modeling platform. Assuming that the climatic conditions in the modern Volga basin area during the Late Glacial Era were close to the current conditions, numerical experiments were carried out to simulate deep freezing of soil throughout the entire territory of the modern Volga basin area. It is shown that under permafrost conditions, the Volga River runoff increases by 15-20% and does not provide a twofold rise in water inflow into the sea, estimated from paleogeographic data. At the same time, the experiments have shown that such extreme inflow of water into the Caspian Sea could be formed under the conditions of deep freezing of soils and in the absence of seasonal thawing of the frozen catchment area, i.e. at a colder climate than the modern one.

How to cite: Gelfan, A. and Kalugin, A.: Permafrost in the Caspian Sea basin in the Late Glacier Era as a possible trigger of the sea transgression: checking the hypothesis using a hydrological model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3812, https://doi.org/10.5194/egusphere-egu21-3812, 2021.

The pre-colonial history of Tonga and West Polynesia still suffers from major gaps because its reconstruction is essentially based on legends left by oral tradition, and by archaeological evidence somehow difficult to interpret. By the fourteenth century, the powerful Tu'i Tonga kingdom united the islands of the Tongan archipelago under a centralised authority and, according to tradition, extended its influence to neighbouring island groups in the Central Pacific. However, some periods of deep crisis were identified, e.g. in the mid- 15^th century, marked by an abrupt cessation of inter-archipelago migration on the deep seas in the Pacific, significant cultural changes, and a decrease in accessible natural resources. The origins of these disturbances are still debated, and are usually assigned to internal political problems or loss of external influence vis-à-vis neighboring states. However, the hypothesis of a major natural disaster was never suggested up to now.

Drawing on a body of new evidence from sedimentary signatures and radiocarbon dating of charcoal and marine bioclasts, geomorphology, and sedimentology, in support of previously published archaeological data, we argue that the Tu’i Tonga kingdom was severely impacted by a megatsunami in the mid-15th century. We also discuss the likely sources of this event, which happened in an isolated region of the world before the European maritime “great discoveries”. This tsunami could be the source of vivid local myths that strongly suggest that a giant wave covered almost the entire island of Tongatapu at one time.

How to cite: Lavigne, F., Morin, J., Patrick, W., Olivier, W., Taaniela, K., Maea, A. V., Kelfoun, K., Mokadem, F., Paris, R., Malawani, M. N., Audrey, F., Benbakkar, M., Saulnier-Copard, S., Vidal, C. M., Tu’I’afitu, T., Christopher, G., and Kitekei’aho, F.: The kingdom of Tonga devastated by a megatsunami in the mid-15th century, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5317, https://doi.org/10.5194/egusphere-egu21-5317, 2021.

In France, flooding is the most common and damaging natural hazard. Due to global warming, it is expected to globally exacerbate, and it could be even more pronounced in the European Alps that warm at a rate twice as high in the Northern Hemisphere. The Alps are densely populated, increasing exposure and vulnerability to flood hazard. To approach long-term evolutions of past flood occurrence and related socio-economic impacts in relation to changes in the flood risk components (i.e. hazard, exposure and vulnerability), the study of historical records is highly relevant.

To this aim we build and analyze the newly constituted database of Historical Impacts of Floods in the Arve Valley (HIFAVa), located in French Northern Alps and starting in 1850. The database reports flood occurrences and impacts in a well-documented Alpine catchment that encompasses both a hydrological and societal diversity.

We analyze past impacts in regard to their characteristics and evolution in both time and space. Our results show an increasing occurrence of impacts from 1920 onwards, which is more likely related to indirect source effects and/or increasing exposure of goods and people rather than hydrological changes. The analysis reveals that small mountain streams and particularly glacial streams caused more impacts (67%) than the main river. While increase in heavy rainfall and ice melt are expected to enhance flood hazard in small Alpine catchments, this finding calls to pay a particular attention to flood risk assessment and management in small catchments.

How to cite: Boisson, E., Wilhelm, B., Garnier, E., Mélo, A., Anquetin, S., and Ruin, I.:  Geo-historical analysis of flood impacts in a large Alpine catchment (Arve River, French Alps, 1850 – 2015)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4720, https://doi.org/10.5194/egusphere-egu21-4720, 2021.

Large landslides have affected the geomorphological evolution of most Alpine territories. Some catastrophic events also had a huge impact on the economic and cultural development of human societies. In the Bregaglia Valley and in nearby territories, evidences of settlements date back to the Roman age. In these areas, human activities always coexisted with the natural evolution of the valley, which has been characterized by recurrent natural events such as floods and landslides. Among these, the 1618 Piuro landslide was the one with the strongest impact, remaining impressed on the collective imagination and artistic representations. It erased an entire village and its 1000-2000 inhabitants few km East of Chiavenna, and it is still remembered as one of the worst tragedies in the history of the region. Understanding the evolutionary dynamics of such a geomorphologically active landscape, taking notes from the ancient or recent past, plays a central role in risk assessment and mitigation. In Piuro, such dynamics were investigated through a multidisciplinary approach, starting from the historical and archaeological analyses of the event and involving: (i) the geological/geomorphological characterization of the Last Glacial Maximum, to present palimpsest landscape of the valley through the realization of thematic maps, (ii) the stratigraphic interpretation of new boreholes crossing the landslide deposits and the deeper intra-mountain sedimentary valley fill, (iii) the realization of topographic, petrographic, geophysical (HVSR and MASW) and geo-mechanical surveys. In addition, the implementation of numerical models is on the way, to check different hypotheses on the predisposing factors, triggers, timing and evolution of the 1618 Piuro landslide. To increase the awareness of natural hazards in mountain settings and to promote a risk and resilience culture, all these acquired knowledge will be disseminated and shared with citizen, authorities and scientists in the frame of the Interreg project A.M.AL.PI.18. The fulfilment of a transboundary (Italian-Swiss) geo-cultural path will link other sites of historical and geological relevance through the territories of Bregaglia, Valchiavenna, Moesa and Ticino. Showing and telling the history of catastrophic landslides and their impacts on the involved communities, it will contribute to enhance the perception of beauty and the awareness of geo-hazard. The dissemination of knowledge and awareness is one main goal towards risk mitigation.

The present work was co-funded through the EU, Regional Development European Fund, by Italian State, Helvetic Confederation and Cantons under the Interreg V-A IT-CH 2014-2020 Cooperation Program - A.M.AL.PI.2018 “Alpi in Movimento, Movimento nelle Alpi. Piuro 1618-2018", ID 594274 – Axis 2 “Cultural and natural enhancement”.

How to cite: Pigazzi, E., Apuani, T., Bersezio, R., Camera, C., Comunian, A., Lualdi, M., and Morcioni, A.: A multidisciplinary approach to improve and share the understanding of landslide hazard in mountain environments: the PIURO 1618 disaster, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14567, https://doi.org/10.5194/egusphere-egu21-14567, 2021.

To a large extent, the temporal definition of an extreme event depends on the context and the level of analysis that we are able to deploy. It should be massive and concentrated compared to the challenges a system is facing on everyday basis, it should provide a shock, and it should require major efforts to absorb its impacts. On historical timescales, extreme events happen over hours, days, months, at the longest, years. Compared to the process through which environmental archives develop, these are very short timescales, possibly with no chance of being recorded in the sediments. However, if we consider that an extreme event should have massive impacts, and these should be last for longer than the event itself, there is a good chance we could actually observe the environmental change associated with the extreme event in the sediments.

In my talk, I will look at two plague pandemics – the first, 6^th-8^th c. AD, and the second, 14^th-18^th c. AD – and their initial outbreaks (known as the Justinianic Plague and the Black Death) in order to see their reflection in the sediments throughout Europe and the Mediterranean, primarily in the pollen data. As I will demonstrate, in some cases the impact was minimal, barely visible, while in others it was indeed massive. This will bring me back to the definition of the extreme event: is it possible to have an extreme event that did not have any impact? Can the same event – the spread of a new pathogen, in our case – become extreme in one social-geographical context and not in another?

How to cite: Izdebski, A.: Extreme events at historical time-scales: are they visible in the paleoenvironmental records?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9195, https://doi.org/10.5194/egusphere-egu21-9195, 2021.