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1.
A cryptotephra layer from the eruption of Hekla in 1947 has recently been discovered in Irish peatlands. This tephra layer represents the most recent deposition of volcanic ash in the UK prior to the eruption of Eyjafjallajökull in 2010. Here we examine the concentration and geochemistry of the Hekla 1947 tephra in 14 peat profiles from across Northern Ireland. Electron probe microanalysis of individual tephra shards (n = 91) reveals that the tephra is of dacitic–andesitic geochemistry and is highly similar to the Hekla 1510 tephra, although spheroidal carbonaceous particle profiles can be used for successful discrimination of the two layers. The highest concentrations of Hekla 1947 are found in western sites, probably reflecting the pathway of the ash fall event due to the prevailing wind direction. Comparable tephra concentrations from two cores (1 km apart) from a single bog and from nearby sites may suggest that tephra shard concentrations in peat profiles reflect ash fallout densities across a specific region, rather than site‐specific factors associated with peatlands. This paper firmly establishes Hekla 1947 as a useful chronostratigraphic marker for the twentieth century, although within a restricted zone. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

2.
The Eyjafjöll AD 2010 eruption is an extraordinary event in that it led to widespread and unprecedented disruption to air travel over Europe – a region generally considered to be free from the hazards associated with volcanic eruptions. Following the onset of the eruption, satellite imagery demonstrated the rapid transportation of ash by westerly winds over mainland Europe, eventually expanding to large swathes of the North Atlantic Ocean and the eastern seaboard of Canada. This small‐to‐intermediate size eruption and the dispersal pattern observed are not particularly unusual for Icelandic eruptions within a longer‐term perspective. Indeed, the Eyjafjöll eruption is a relatively modest eruption in comparison to some of the 20 most voluminous eruptions that have deposited cryptotephra in sedimentary archives in mainland Europe, such as the mid Younger Dryas Vedde Ash and the mid Holocene Hekla 4 tephra. The 2010 eruption, however, highlights the critical role that weather patterns play in the distribution of a relatively small amount of ash and also highlights the spatially complex dispersal trajectories of tephra in the atmosphere. Whether or not the preservation of the Eyjafjöll 2010 tephra in European proxy archives will correspond to the extensive distributions mapped in the atmosphere remains to be seen. The Eyjafjöll 2010 event highlights our increased vulnerability to natural hazards rather than the unparalleled explosivity of the event. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

3.
Large Plinian eruptions from Hekla volcano, Iceland, produce compositionally zoned tephra used as key markers in tephrochronology. However, spatial variations in chemical composition of a tephra layer may complicate its identification. An example is the 5950–6180 cal a bp Hekla Ö tephra layer, which shows compositional spread from rhyolite, dacite and andesite to basalt. In soil sections north of Hekla, the SiO2 content of the tephra glass reaches 76 wt% in the lowest unit of the Hekla Ö deposit and decreases to 62–63 wt% in the uppermost unit. Intermingled within the whole deposit are basalt tephra grains having 46–47 wt% SiO2. The composition of the basalt glass includes primitive basalt and a more evolved basalt (MgO >6 and <6 wt%, respectively). Together with literature data, the Hekla Ö tephra and the so-called T-Tephra/Hekla-T are most likely from contemporaneous eruptions of different vents on the Hekla volcanic system, forming a single important marker tephra (Hekla ÖT) deposited over 80% of Iceland. Identification is complicated by its spatial compositional heterogeneity, such as systematic decrease in SiO2 content from the east to the west of Hekla volcano. Consequently, an individual tephra layer from a large explosive eruption can have different composition at different locations. © 2020 John Wiley & Sons, Ltd.  相似文献   

4.
Hekla volcano is a major producer of large, widespread silicic tephras. About 3000 years ago, the dominant eruption mode shifted from infrequent large (>1 km3) to more frequent moderate (<1 km3) eruptions. In the following two millennia ≥20 explosive silicic-to-intermediate eruptions occurred, and six or more basaltic. Three categories can be identified with dacite/andesite to basaltic andesite in the oldest eruptions through basaltic andesite to basalt in the youngest eruptions. Ten tephra layers of the first category have distinct field characteristics: a pale lower unit and a dark upper unit (two coloured or TC-layers). Colour separation is sharp indicating a stratified magma chamber origin. The lower unit is dominantly andesitic (61–63% SiO2), while the upper unit is basaltic andesite (53–57% SiO2). Volumes of the eight largest TC-layers range from 0.2 to 0.7 km3 as freshly fallen. Radiocarbon and soil accumulation rate dates constrain the TC-layers to between 3000 and 2200 years ago. Two of these (~2890 and ~2920 b2k) are likely to occur overseas. Low SiO2 in the last erupted tephra of the TC-layers is comparable to that of historical Hekla lavas, implying a final effusive phase. The Hekla edifice may, consequently, be younger than 3000 years.  相似文献   

5.
Volcanic ash can disperse thousands of kilometres from the source volcano and provide valuable chronostratigraphic markers for palaeoclimate studies. We present new cryptotephra findings of historical and modern Icelandic eruptions in annually laminated lacustrine sediment records from several sites within a 570 km SW–NE transect across northern Poland. Sediments from the two lakes Wąsoskie and Szurpiły contain glass shards originating from the Plinian Askja ad 1875 eruption and showing bimodal, rhyolitic and dacitic affinities. A further cryptotephra finding in Lake Lubińskie suggests a potential origin from the Hekla ad 1845 eruption. These new findings extend the tephra dispersal map towards the south-east and provide valuable isochrons for the synchronisation of palaeoclimate proxy data at the termination of the Little Ice Age in central eastern Europe. Very low glass concentrations of modern cryptotephra in Lake Wąsoskie were potentially correlated with the Eyjafjallajökull ad 2010 eruption. Further findings in the uppermost sediments of lakes Szurpiły and Żabińskie in north-eastern Poland tentatively suggest other sources from either the Hekla and/or Kamchatkan volcanoes.  相似文献   

6.
A Holocene tephra record from the Lofoten Islands, Arctic Norway   总被引：2，自引：0，他引：2  
Pilcher, J., Bradley, R. S., Francus, P. & Anderson, L. 2005 (May): A Holocene tephra record from the Lofoten Islands, Arctic Norway. Boreas , Vol. 34, pp. 136–156. Oslo. ISSN 0300–9483.
A tephrochronology has been established for a peat bog in the Lofoten Islands that provides a dating framework for future lake and bog studies of climate variation in this climatically sensitive area. Twenty-three tephra layers were identified, all apparently of Icelandic origin. These included the historically dated tephras of AD 1875 (Askja), AD 1362 (Öraefajökull), AD 1158 (Hekla), AD 1104 (Hekla) and the Landnam tephra identified at AD 875 in the GRIP ice core. Other layers, previously radiocarbon dated in Ireland and elsewhere, include the Hekla eruptions of c. 2310 BC and c. 5990 BC. The basal clays below the peat contain tephra of both the Askja eruption of c. 9500 BC (10 000 radiocarbon years BP) and the well-known Vedde Ash of c. 12 000 BP (10 030 80 BC in GRIP ice core).  相似文献   

7.
Far-travelled ash layers from explosive volcanic eruptions can provide invaluable marker horizons for dating and correlating regional to global sedimentary archives. Here, we present a new cryptotephra associated with the ~5.9 cal ka bp Towada-Chuseri eruption (To-Cu) in a peat sediment record from northeast China. This tephra exhibits a rhyolitic glass composition that can be distinguished from other widespread tephra layers around the region of Japan and northeast China. Our findings extend the known range of this ash significantly, making it now traceable about 1200 km from its source, Towada volcano, Japan. Notably, this tephra provides an important isochron for synchronising palaeoenvironmental studies during the mid-Holocene period from the western Pacific, central Japan, Japan Sea and northeast China.  相似文献   

8.
《第四纪科学杂志》2017,32(4):457-462
Despite the discovery of cryptotephra layers in over 100 peatlands across northern Europe, Holocene cryptotephra layers have not previously been reported from Polish peatlands. Here we present the first Holocene tephra findings from two peatlands in northern Poland. At Bagno Kusowo peatland we identify the most easterly occurrence of the AD 860 B tephra, recently correlated to the White River Ash (WRAe) derived from Mount Churchill, Alaska. A shorter core from Linje peatland contains tephra from the Askja 1875 eruption, extending the spatial distribution and regional importance of this Icelandic tephra in Eastern Europe. Our research indicates the potential of cryptotephra layers to date and correlate the growing number of palaeoenvironmental studies being conducted on Polish peatlands and contributes towards the development of a regional Holocene tephrostratigraphy for Poland. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons, Ltd.
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9.
Tephra layers with Icelandic provenance have been identified across the North Atlantic region in terrestrial, lacustrine, marine and glacial environments. These tephra layers are used as marker horizons in tephrochronology including climate studies, archaeology and environmental change. The major element chemistries of 19 proximally deposited Holocene Icelandic silicic tephra layers confirm that individual volcanic systems have unique geochemical signatures and that eruptions from the same system can often be distinguished. In addition, glass trace element chemistry highlights subtle geochemical variations between tephra layers which appear to have identical major element chemistry and thus allows for the identification of some, if not all, tephra layers previously considered identical in composition. This paper catalogues the compositional variation between the widespread Holocene Icelandic silicic tephra deposits.  相似文献   

10.
The volcanic ash or ‘tephra’ cloud resulting from the relatively small (volume and VEI) eruption of the Icelandic volcano Eyjafjallajökull in 2010 caused major air travel disruption, at substantial global economic cost. On several occasions in the past few centuries, Icelandic eruptions have created ash and/or sulphur dioxide clouds which were detected over Europe (e.g. Hekla in 1947, Askja in 1875, and Laki in 1783). However, these historical observations do not represent a complete record of events serious enough to disrupt aviation in Europe. The only feasible evidence for this is within the geological tephra record. Ash layers are preserved in bogs and lakes where tephra deposited from the atmosphere is incorporated in the peat/mud. In this article we: 1, introduce the analysis of the Northern European sedimentary tephra record; 2, discuss our findings and modelling results; 3, highlight how these were misinterpreted by the popular media; and 4, use this experience to outline several existing problems with current tephra studies and suggest agendas for future research.  相似文献   

11.
The generation of reliable age models for palaeoenvironmental and archaeological records in the Eurasian Arctic is often problematic when using conventional dating techniques. Tephrochronology can potentially improve the chronologies of such records and synchronise disparate sedimentary archives. However, to date, systematic tephra studies are lacking for this region. This paper presents the first cryptotephra data from the White Sea region (northwestern Russia) based on a peat core spanning the past ~1800 years. We identify seven geochemical glass populations that derive from six Icelandic volcanoes and correlate four of them to north European tephra isochrons; these include Askja ad 1875, the basaltic component of the ad 877 Landnám tephra, and tephras BTD-15 (c. ad 1750–1650) and SL-2/SB-2 (ad 803–767) from unknown eruptions of Katla and Snæfellsjökull, respectively. The remaining three populations originate from Grímsvötn, Hekla and Katla; however, their attribution to individual eruptions remains ambiguous. These findings highlight the potential to extend the Late Holocene tephrochronological framework of northern Europe to the west Eurasian Arctic. The detection of at least three basaltic tephras in the core suggests that basaltic shards can be transported over larger distances than previously known and that peatlands are well suited to preserve such components.  相似文献   

12.
This paper presents one of the most extensive Holocene tephra records found to date in Scandinavia. Microtephra horizons originating from Icelandic eruptions were recorded in two ca. 2 m thick peat profiles at Klocka Bog in west‐central Sweden. Five of the microtephra horizons were geochemically correlated to the Askja‐1875, Hekla‐3, Kebister, Hekla‐4 and Lairg A tephras respectively. Radiocarbon‐based dating of these tephras broadly agree with previously published ages from Iceland, Sweden, Germany and the British Isles. The identification of the Lairg A tephra demonstrates a more widespread distribution than previously thought, extending the usefulness of Icelandic Holocene tephrochronology further north into west‐central Scandinavia. Long‐lasting snow cover and seasonal wind distribution in the lower stratosphere are suggested as factors that may be responsible for fragmentary tephra deposition patterns in peat deposits of subarctic Scandinavia. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

13.
Comparatively few Icelandic tephra horizons dated to the early part of the Holocene have so far been detected outside Iceland. Here, I present several tephra horizons that have been recorded in a Holocene peat sequence on the Faroe Islands. Geochemical analyses show that at least two dacitic and one rhyolitic tephra layers were erupted from the Katla volcanic system on southern Iceland between ca. 8000 and 5900 cal. yr BP. The upper two layers can be correlated with the SILK tephras described from southern Iceland, whereas the third, dated to ca. 8000 cal. yr BP, has a geochemistry virtually identical to the rhyolitic component of the Vedde Ash. The results suggest that the Late Weichselian and early Holocene eruption history of the Katla volcano was probably more complex than inferred from Iceland. A new, early Holocene rhyolitic tephra dated to ca. 10 500 cal. yr BP probably originates in the Snæfellsnes volcanic centre in western Iceland. These new findings may play an important role in developing a Holocene tephra framework for northwest Europe. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

14.
Nine tephra layers in marine sediment cores (MD99‐2271 and MD99‐2275) from the North Icelandic shelf, spanning the Late Glacial and the Holocene, have been investigated to evaluate the effectiveness of methods to detect tephra layers in marine environments, to pinpoint the stratigraphic level of the time signal the tephra layers provide, and to discriminate between primary and reworked tephra layers in a marine environment. These nine tephra layers are the Borrobol‐like tephra, Vedde Ash, Askja S tephra, Saksunarvatn ash, and Hekla 5, Hekla 4, Hekla 3, Hekla 1104 and V1477 tephras. The methods used were visual inspection, magnetic susceptibility, X‐ray photography, mineralogical counts, grain size and morphological measurements, and microprobe analysis. The results demonstrate that grain size measurements and mineralogical counts are the most effective methods to detect tephra layers in this environment, revealing all nine tephra layers in question. Definition of the tephra layers revealed a 2–3 cm diffuse upper boundary in eight of the nine tephra layers and 2–3 cm diffuse lower boundary in two tephra layers. Using a multi‐parameter approach the stratigraphic position of a tephra layer was determined where the rate of change of the parameters tested was the greatest compared with background values below the tephra. The first attempt to use grain morphology to distinguish between primary and reworked tephra in a marine environment suggests that this method can be effective in verifying whether a tephra layer is primary or reworked. Morphological measurements and microprobe analyses in combination with other methods can be used to identify primary tephra layers securely. The study shows that there is a need to apply a combination of methods to detect, define (the time signal) and discriminate between primary and reworked tephra in marine environments. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
Kamchatka Peninsula is one of the most active volcanic regions in the world. Many Holocene explosive eruptions have resulted in widespread dispersal of tephra-fall deposits. The largest layers have been mapped and dated by the 14C method. The tephra provide valuable stratigraphic markers that constrain the age of many geological events (e.g. volcanic eruptions, palaeotsunamis, faulting, and so on). This is the first systematic attempt to use electron microprobe (EMP) analyses of glass to characterize individual tephra deposits in Kamchatka. Eighty-nine glass samples erupted from 11 volcanoes, representing 27 well-identified Holocene key-marker tephra layers, were analysed. The glass is rhyolitic in 21 tephra, dacitic in two, and multimodal in three. Two tephra are mixed with glass compositions ranging from andesite/dacite to rhyolite. Tephra from the 11 eruptive centres are distinguished by their glass K2O, CaO, and FeO contents. In some cases, individual tephra from volcanoes with multiple eruptions cannot be differentiated. Trace element compositions of 64 representative bulk tephra samples erupted from 10 volcanoes were analysed by instrumental neutron activation analysis (INAA) as a pilot study to further refine the geochemical characteristics; tephra from these volcanoes can be characterized using Cr and Th contents and La/Yb ratios.

Unidentified tephra collected at the islands of Karaginsky (3), Bering (11), and Attu (5) as well as Uka Bay (1) were correlated to known eruptions. Glass compositions and trace element data from bulk tephra samples show that the Karaginsky Island and Uka Bay tephra were all erupted from the Shiveluch volcano. The 11 Bering Island tephra are correlated to Kamchatka eruptions. Five tephra from Attu Island in the Aleutians are tentatively correlated with eruptions from the Avachinsky and Shiveluch volcanoes.  相似文献   

16.
The discovery of sites preserving tephra layers from multiple volcanic centres is key to constructing a single European tephrostratigraphic framework for the Late Quaternary. Until now, the tephrostratigraphy of Europe has been divided into two halves: sites in the North Atlantic and northern Europe regions link the Icelandic, Eifel, and the Massif Central volcanic histories; whilst sites in southern Europe record the sequence of tephra layers produced by circum-Mediterranean volcanic provinces. The missing link, able to tie together these two halves, is found in the tephrostratigraphic record of Lake Bled, Slovenia.Lake Bled, in the Julian Alps, Slovenia, holds a high resolution multi-proxy palaeoenvironmental archive for the Lateglacial of south-central Europe. Cryptotephra investigations have revealed three tephra layers: two closely spaced within Younger Dryas stadial sediments and one shortly after the start of the Bølling-Allerød interstadial warming. Two of the tephra layers (Bld_T120 and Bld_T240) are of Campanian origin and are correlated to deposits of the Pomici Principali (PP) and Neapolitan Yellow Tuff (NYT) eruptions, respectively. The third layer (Bld_T122) correlates to the Icelandic Vedde Ash (VA), extending the known fallout of this widespread marker layer farther to the southeast.The Lake Bled record also allows the stratigraphic relationship and relative ages of the VA and the PP eruption to be discerned for the first time. Whilst existing numerical age estimates for these two deposits are indistinguishable within errors, their close occurrence in the same lacustrine sediment sequence shows that the VA was erupted shortly prior to the PP eruption.The tephrostratigraphy of Lake Bled developed here helps us to tie together regional volcanic stratigraphies into a broader, continental-scale lattice of sites, with the potential to allow the transfer of dates between remote sequences and the construction of relative chronologies, beneficial in particular for environmental and archaeological research.  相似文献   

17.
A combination of AMS14C dating and tephrochronology has been used to date late Holocene oceanographic events in a 335 cm marine record, covering about 4600 cal. yr with sedimentation rates exceeding 80 cm 1000 yr−1. The core site is located 50 km offshore on the northern Icelandic shelf. Tephra markers from Iceland serve to correlate the marine and terrestrial records. Especially notable is the presence of three geochemically correlated tephra markers from the Icelandic volcano Hekla (Hekla 4, Hekla 3 and Hekla 1104). Benthic and planktonic foraminiferal abundance and distribution as well as the petrography of the sand fraction of the muddy shelf sediments are used as palaeoceanographic proxies. The foraminiferal assemblages reflect a general cooling trend during the last 4600 yr. A marked drop in sea‐surface temperatures is registered at about 3000 cal. yr BP, corresponding to the level of the Hekla 3 tephra. There is faunal indication of temperature amelioration during the Medieval Warm Period and a cooling again during the Little Ice Age. Periods of ice rafting events are indicated by ice rafted debris (IRD) concentrations, e.g. at around 3000 cal. yr BP and during the Little Ice Age. The former event occurred just prior to the deposition of the Hekla 3 tephra marker, the largest Holocene Hekla eruption. A correlation with terrestrial climatic events in Iceland is presented. A standard marine reservoir correction of 400 14C yr appears to be reasonable, at least during periods with high influence of water masses from the Irminger Current on the northern Icelandic shelf. An increase to ca. 530 14C yr may have occurred, however, when water masses derived from the East Greenland Current were dominant in the area. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

18.
A tephra record is presented for a sediment core from Llyn Llech Owain, south Wales, spanning the early- to mid-Holocene. Seven cryptotephra deposits are discovered with three thought to correlate with known eruptions and the remaining four considered to represent previously undocumented events. One deposit is suggested to correlate with the ~6.9 cal ka bp Lairg A tephra from Iceland, whereas more distant sources are proposed as the origin for two of the tephra deposits. A peak of colourless shards in early-Holocene sediments is thought to tentatively correlate with the ~9.6 cal ka bp Fondi di Baia tephra (Campi Flegrei) and a second cryptotephra is tentatively correlated with the ~3.6 cal ka bp Aniakchak (CFE) II tephra (Alaska). The Fondi di Baia tephra has never been recorded beyond proximal sites and its discovery in south Wales significantly extends the geographical distribution of ash from this eruption. The remaining four cryptotephra deposits are yet to be correlated with known eruptions, demonstrating that our current understanding of widespread tephra deposits is incomplete. This new tephra record highlights the potential for sites at more southerly and westerly locations in northwest Europe to act as repositories for ash from several volcanic regions.  相似文献   

19.
Volcanic ash preserved in marine sediment sequences is key for independent synchronization of palaeoclimate records within and across different climate archives. Here we present a continuous tephrostratigraphic record from the Labrador Sea, spanning the last 65–5 ka, an area and time period that has not been investigated in detail within the established North Atlantic tephra framework. We investigated marine sediment core GS16-204-22CC for increased tephra occurrences and geochemically analysed the major element composition of tephra shards to identify their source volcano(es). In total we observed eight tephra zones, of which five concentration peaks show isochronous features that can be used as independent tie-points in future studies. The main transport mechanism of tephra shards to the site was near-instantaneous deposition by drifting of sea ice along the East Greenland Current. Our results show that the Icelandic Veidivötn volcanic system was the dominant source of tephra material, especially between late Marine Isotope Stage (MIS) 4 and early MIS 3. The Veidivötn system generated volcanic eruptions in cycles of ca. 3–5 ka. We speculate that the quantity of tephra delivered to the Labrador Sea was a result of variable Icelandic ice volume and/or changes in the transportation pathway towards the Labrador Sea.  相似文献   

20.
 Eruptions from Ruapehu Volcano on 11 and 14 October 1995 and 17 June 1996 distributed at least 36×106 m3 of sulphur(S)-rich tephra over the central and eastern North Island of New Zealand. The tephras added between 30–1500 kg ha–1 S to at least 25 000 km2 of land in primary production. Smaller but beneficial amounts of selenium (Se) and in some areas potassium and magnesium were also supplied. Addition of S to the soils in the form of sulphate and elemental S resulted in a drop in soil pH and an increase in pasture S contents within seven weeks of the eruptions. The soils affected by the tephra are naturally low in S and Se, but following the eruptions S was not required in fertilizer applications in many areas. The strongest and longest lasting effects of S and Se deposition were in high anion-retention soils particularly Hapludands (moist, moderately weathered soils, derived from volcanic ash). Soluble fluorine concentrations within the tephras were low compared to historic Icelandic and Chilean examples. However, pastoral livestock deaths were apparently caused by fluorosis in addition to starvation when tephra covered feed. The Ruapehu tephra contained very low concentrations of other soluble toxic elements. Received: 17 January 1997 · Accepted: 31 March 1997  相似文献   

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