22 research outputs found
Recommended from our members
Bridging Legends and Science: Field Evidence of a Large Tsunami that Affected the Kingdom of Tonga in the 15th Century
The pre-colonial history (i.e. before the 16th century) of Tonga and West Polynesia still suffers from major gaps despite significant scientific advances in recent years, particularly in the field of archaeology. By the 14th century, the powerful Tuâi 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- 15th 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 they are usually assigned to internal political problems or loss of external influence vis-Ă -vis neighboring chiefdoms. However, the hypothesis of a major natural disaster was rarely suggested up to now, while field evidence points to the occurrence of a very large tsunami in the past, including the presence of numerous megablocks that were deposited by a âred waveâ (orpeau kula, which also mean tsunami in the Tongan language) according to a local myth. 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 a large tsunami inundated large areas of Tongatapu island in the mid-15th century with runup heights up to 30Â m, and that the Tuâi Tonga kingdom was severely impacted by this event. We also discuss the likely sources of this tsunami.</jats:p
Large volcanic landslide and debris avalanche deposit at Meru, Tanzania
International audienc
Lithium isotope fractionation during magma degassing: Constraints from silicic differentiates and natural gas condensates from Piton de la Fournaise volcano (RĂ©union Island)
International audienceRecent volcanic products from the Piton de la Fournaise Volcano, Reunion, show pronounced depletion or enrichment in lithium and significant isotopic fractionation related to degassing. (1) trachytic pumices from the April 2007 eruption show extreme Li depletion (90%) and isotopic fractionation (ÎŽ7Li of â 21â°). The depletion of water and volatiles (Cl, F, B, Cs) in these samples suggests that Li loss occurred in response to degassing, which most likely occurred as the small, isolated volume of magma underwent extensive differentiation near the surface. Because the pre-degassing composition is relatively well known, the composition of the degassed pumice constrains the partition coefficient to 60 < DVâM < 135 and the isotopic fractionation factor, αVâM, to 1.010 at magmatic temperatures. Unlike DVâM, αVâM does not depend on whether crystallization and degassing occurred successively or concomitantly. (2) basaltic samples from the interior wall of the long-lived 1998 Piton Kapor were extensively altered by acidic gas. They also show extreme Li depletion, but barely significant isotopic fractionation (ÎŽ7Li = + 4.5â°), suggesting that high-temperature leaching of Li by volcanic gas does not significantly fractionate Li isotopes. (3) high-temperature (400â325 °C) gas condensates formed during degassing of the thick lava flow of April 2007 display high Li contents (50â100 ppm), which are consistent with Li being as volatile as Zn and Sn. Their isotopically light Li signature (average of â 1.7â°) is consistent with their derivation from isotopically heavy vapor (+ 13.5â°) if the factor of isotopic fractionation between condensate and vapor is less than 0.985. A degassing-crystallization model accounts for the evolution of trace species, which, like lithium, are volatile but also moderately incompatible
Hadean protocrust reworking at the origin of the Archean Napier Complex (Antarctica)
International audienceThe origin of the first continents is still poorly constrained due to the great scarcity of >3.7 Ga rocks. The Napier Complex (East Antarctica) hosts such rocks but the extreme metamorphic conditions it experienced have compromised most isotopic systematics. Here we have studied Mount Sones and Gage Ridge orthogneisses from the Napier complex using microbeam (LA-MC-ICP-MS) U-Pb and Lu-Hf isotope measurements in zircon, together with 146,147Sm-143,142Nd isotope systematics in the corresponding whole rocks to uncover primary information about their origin. Our U-Pb results reveal that these orthogneisses formed at 3794 ± 40 and 3857 ± 39 Ma, respectively, by reworking of 4456-4356 Ma mafic protocrust, as testified to by 176Lu-176Hf and 147,146Sm-143,142Nd systematics. Other Eoarchean terranes in Greenland, Canada, and China also show involvement of Hadean crust(s) in their formation which suggests that protocrusts were massively reworked to form new continents around the Hadean-Eoarchean boundary. Such a mechanism would account for the absence of early-formed protocrust from the geological record despite recent models proposing rapid crustal growth in the Hadean (~25 % of present day volume or surface)
Historical fluvial palaeodynamics and multi-proxy palaeoenvironmental analyses of a palaeochannel, Allier River, France
International audienc
Integrating field, textural, and geochemical monitoring to track eruption triggers and dynamics: a case study from Piton de la Fournaise
The 2014 eruption at Piton de la Fournaise (PdF), La RĂ©union, which
occurred after 41 months of quiescence, began with surprisingly little
precursory activity and was one of the smallest so far observed at PdF in
terms of duration (less than 2 days) and volume (less than 0.4âŻâĂââŻ106âŻm3).
The pyroclastic material was composed of golden basaltic pumice
along with fluidal, spiny iridescent and spiny opaque basaltic scoria.
Density analyses performed on 200 lapilli reveal that while the spiny opaque
clasts are the densest (1600âŻkgâŻmâ3) and most crystalline (55âŻvol.âŻ%), the golden pumices are the least dense (400âŻkgâŻmâ3) and
crystalline (8âŻvol.âŻ%). The connectivity data indicate that the fluidal
and golden (Hawaiian-like) clasts have more isolated vesicles (up to 40âŻvol.âŻ%) than the spiny (Strombolian-like) clasts (0â5âŻvol.âŻ%). These
textural variations are linked to primary pre-eruptive magma storage
conditions. The golden and fluidal fragments track the hotter portion of the
melt, in contrast to the spiny fragments and lava that mirror the cooler
portion of the shallow reservoir. Exponential decay of the magma ascent and
output rates through time revealed depressurization of the source during
which a stratified storage system was progressively tapped. Increasing
syn-eruptive degassing and meltâgas decoupling led to a decrease in the
explosive intensity from early fountaining to Strombolian activity. The
geochemical results confirm the absence of new input of hot magma into the
2014 reservoir and confirm the emission of a single shallow, differentiated
magma source, possibly related to residual magma from the November 2009
eruption. Fast volatile exsolution and crystalâmelt separation (second
boiling) were triggered by deep pre-eruptive magma transfer and stress field
change. Our study highlights the possibility that shallow magma pockets can
be quickly reactivated by deep processes without mass or energy (heat)
transfer and produce hazardous eruptions with only short-term elusive
precursors.</p
The kingdom of Tonga devastated by a megatsunami in the mid-15th century
International audienceThe 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- 15th 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-Ă -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 Tuâi 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 âgreat discoveriesâ. 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
The kingdom of Tonga devastated by a megatsunami in the mid-15th century
International audienceThe 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- 15th 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-Ă -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 Tuâi 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 âgreat discoveriesâ. 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