IF 0.9 4区地球科学

Jokull Pub Date : 2021-04-08 DOI: 10.33799/JOKULL2020.70.035

R. Vestergaard, Gro Birkefeldt Møller Pedersen, C. Tegner

{"title":"The 1845–46 and 1766–68 eruptions at Hekla volcano: new lava volume estimates, historical accounts and emplacement dynamics","authors":"R. Vestergaard, Gro Birkefeldt Møller Pedersen, C. Tegner","doi":"10.33799/JOKULL2020.70.035","DOIUrl":"https://doi.org/10.33799/JOKULL2020.70.035","url":null,"abstract":"We use new remote sensing data, historical reports, petrology and estimates of viscosity based on geochemical data to illuminate the lava emplacement flow-lines and vent structure changes of the summit ridge of Hekla during the large eruptions of 1845–46 and 1766–68. Based on the planimetric method we estimate the bulk volumes of these eruptions close to 0.4 km and 0.7 km, respectively. However, comparison with volume estimates from the well-recorded 1947–48 eruption, indicates that the planimetric method appears to underestimate the lava bulk volumes by 40–60%. Hence, the true bulk volumes are more likely 0.5–0.6 km and 1.0–1.2 km, respectively. Estimated melt viscosity averages for the 1766–68 eruption amount to 2.5 × 10 Pa s (pre-eruptive) and 2.5×10 Pa s (degassed), and for the 1845–46 eruption 2.2×10 Pa s (pre-eruptive) and 1.9×10 Pa s (degassed). Pre-eruptive magmas are about one order of magnitude more fluid than degassed magmas. In the 1845–46 and 1947–48 eruptions, SiO2 decreased from 58–57 to 55–54 wt% agreeing with a conventional model that Hekla erupts from a large, layered magma chamber with the most evolved (silicarich) magmas at the top. In contrast, the lava-flows from 1766–68 reveal a more complicated SiO2 trend. The lava fields emplaced in 1766 to the south have SiO2 values 54.9–56.5%, while the Hringlandahraun lava-flow that erupted from younger vents on the NE end of the Hekla ridge in March 1767 has higher SiO2 of 57.8%. This shows that the layered magma chamber model is not suitable for all lava-flows emplaced during Hekla eruptions.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"129 1","pages":"35-56"},"PeriodicalIF":0.9,"publicationDate":"2021-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75074399","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Channels of the glacial river Jökulsá á Breiðamerkursandi 冰川河流Jökulsá brei - ðamerkursandi的河道

IF 0.9 4区地球科学

Jokull Pub Date : 2020-12-15 DOI: 10.33799/JOKULL2020.70.119

Snaevarr Gudmundsson, H. Björnsson

{"title":"Channels of the glacial river Jökulsá á Breiðamerkursandi","authors":"Snaevarr Gudmundsson, H. Björnsson","doi":"10.33799/JOKULL2020.70.119","DOIUrl":"https://doi.org/10.33799/JOKULL2020.70.119","url":null,"abstract":"The glacial river Jökulsá á Breiðamerkursandi drains the Jökulsárlón tidal lagoon (27 km2), in Southeast Iceland. Despite being the shortest glacial outlet (0.6 km), it is among the most voluminous rivers in Iceland, with an estimated average drainage of 250–300 m3/s and has doubled its volume at peak runoff. Until a bridge was established, this was one of Iceland’s\u0000most infamous river and for travellers, cruising on horseback, the greatest obstacle to cross on the main road. The river began shaping its present\u0000channel in the late 19th century but was not permanently settled until the mid-20th century. Before that it used to wander around the fan, occasionally in several branches, or as a single heavy moving water. In\u0000this paper we present a map of its known runoffs and channels that were formed in the 19th and 20th centuries. Few channels were digitized from old maps, but several of those were identified and recorded by the late Flosi Björnsson (1906–1993), a farmer from the Kvísker, who guided travellers across the river before the bridge was built. The Breiðamerkurjökull outlet glacier of Vatnajökull, Southeast Iceland, advanced 10–15 km during the Little Ice Age. During the LIA advance the\u0000wide fan shaped shore in front of Breiðamerkurjökull gradually extended outward by >1 km, mainly due to sediment deposition by the Jökulsá river and few other temporal glacial river branches. At the turn of the 20th century the outlet glacier started to retreat slowly and in the 1930s terminal lakes were formed. With the formation of the Jökulsárlón tidal lagoon river dumping at the shore terminated and was replaced by a progressive\u0000coastal erosion. Currently ca. 0.9 km has eroded off the coast since the 1930s. A 0.65 km wide strip now remains between the coast and Jökulsárlón tidal lagoon, where the Jökulsá river and the remains of its former runway channels are located.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"90 1","pages":"119-128"},"PeriodicalIF":0.9,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84838698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

A national glacier inventory and variations in glacier extent inIceland from the Little Ice Age maximum to 2019 从小冰期最大值到2019年，冰岛全国冰川清查和冰川范围变化

IF 0.9 4区地球科学

Jokull Pub Date : 2020-10-15 DOI: 10.33799/JOKULL.70.001

H. Hannesdóttir, O. Sigurðsson, R. Þrastarson, S. Guðmundsson, J. M. Belart, F. Pálsson, E. Magnússon, S. Víkingsson, T. Jóhannesson

{"title":"A national glacier inventory and variations in glacier extent in\u0000Iceland from the Little Ice Age maximum to 2019","authors":"H. Hannesdóttir, O. Sigurðsson, R. Þrastarson, S. Guðmundsson, J. M. Belart, F. Pálsson, E. Magnússon, S. Víkingsson, T. Jóhannesson","doi":"10.33799/JOKULL.70.001","DOIUrl":"https://doi.org/10.33799/JOKULL.70.001","url":null,"abstract":"Abstract — A national glacier outline inventory for several different times since the end of the Little Ice Age (LIA) in Iceland has been created with input from several research groups and institutions, and submitted to the GLIMS (Global Land Ice Measurements from Space, nsidc.org/glims) database, where it is openly available. The glacier outlines have been revised and updated for consistency and the most representative outline chosen. The maximum glacier extent during the LIA was not reached simultaneously in Iceland, but many glaciers started retreating from their outermost LIA moraines around 1890. The total area of glaciers in Iceland in 2019 was approximately 10,400 km2, and has decreased by more than 2200 km2 since the end of the 19th century (corresponding to an 18% loss in area) and by approximately 750 km2 since ~2000. The larger ice caps have lost 10–30% of their maximum LIA area, whereas intermediate-size glaciers have been reduced by up to 80%. During the first two decades of the 21st century, the decrease rate has on average been approximately 40 km2 a-1. During this period, some tens of small glaciers have disappeared entirely. Temporal glacier inventories are important for climate change studies, for calibration of glacier models, for studies of glacier surges and glacier dynamics, and they are essential for better understanding of the state of glaciers. Although surges, volcanic eruptions and jökulhlaups influence the position of some glacier termini, glacier variations have been rather synchronous in Iceland, largely following climatic variations since the end of the 19th century.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"42 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2020-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77330812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5

Glacier changes by Breiðamerkurjökull and Hoffellsjökull in 2010–2019. 2010-2019年Breiðamerkurjökull和Hoffellsjökull冰川变化。

IF 0.9 4区地球科学

Jokull Pub Date : 2020-02-01 DOI: 10.33799/jokull2019.69.137o

Snaevarr Gudmundsson, H. Björnsson

引用次数: 0

Terminus lakes on the south side of Vatnajökull ice cap, SE-Iceland 冰岛东南部Vatnajökull冰帽南侧的终点湖

IF 0.9 4区地球科学

Jokull Pub Date : 2020-02-01 DOI: 10.33799/jokull2019.69.001

S. Guðmundsson, H. Björnsson, F. Pálsson, E. Magnússon, Þ. Sæmundsson, T. Jóhannesson

{"title":"Terminus lakes on the south side of Vatnajökull ice cap, SE-Iceland","authors":"S. Guðmundsson, H. Björnsson, F. Pálsson, E. Magnússon, Þ. Sæmundsson, T. Jóhannesson","doi":"10.33799/jokull2019.69.001","DOIUrl":"https://doi.org/10.33799/jokull2019.69.001","url":null,"abstract":"Many ice-marginal lakes have formed in front of glacier termini in Iceland in recent decades due to climate warming, particularly at the southern margin of Vatnajökull ice cap where several such lakes grow year-by-year at present. At the same time, most glacier-dammed lakes at the lateral ice margins have shrunk or disappeared because of glacier thinning, and jökulhlaups released from them have become smaller. This paper describes changes in glacial lakes in SE-Iceland, from Skeiðarárjökull west of Öræfi to Hoffellsjökull in Hornafjörður. Lakes started to form in front of several glaciers in this area in the 1930s but most did not grow much until the 1990s, except for Jökulsárlón by Breiðamerkurjökull, which has grown steadily since before the middle of the last century. Currently, there are growing terminus lakes by all the main south-flowing outlet glaciers of Vatnajökull, with a combined area of ~60 km2. The subglacial landscape upstream of the termini indicates that the lakes will continue to grow in the coming decades as a consequence of glacier downwasting\u0000if the climate warms as projected. These lakes affect the ice flow and the mass and energy balance of the respective glaciers because of their effect on the force balance of the terminus region, the calving of ice into the lakes, and the absorption of heat spent for melting of calved ice fragments and the terminus ice front. The lakes can cause hazard to settlements and travellers in the adjacent area, as landslides on the glaciers that propagate into the lakes can create tsunami waves with a high run-up and sudden, very dangerous flash floods in the glacier forelands.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"17 1","pages":"1-34"},"PeriodicalIF":0.9,"publicationDate":"2020-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80034255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 17

Glacier variations 1930–1970, 1970–1995, 1995–2017 and 2017–2018

IF 0.9 4区地球科学

Jokull Pub Date : 2020-02-01 DOI: 10.33799/jokull2019.69.129o

H. Hannesdóttir

引用次数: 1

A 25.6 m long firn core extracted from the Grímsvötn ice shelfin June 1993 1993年6月从Grímsvötn冰架提取的25.6米长的铁芯

IF 0.9 4区地球科学

Jokull Pub Date : 2020-02-01 DOI: 10.33799/jokull2019.69.157o

M. Gudmundsson, J. Hólmjárn

引用次数: 0

Historical accounts of pre-eruption seismicity of Katla, Hekla, Öræfajökull and other volcanoes in Iceland Katla, Hekla， Öræfajökull和冰岛其他火山爆发前地震活动的历史记录

IF 0.9 4区地球科学

Jokull Pub Date : 2020-02-01 DOI: 10.33799/jokull2019.69.035

P. Einarsson

{"title":"Historical accounts of pre-eruption seismicity of Katla, Hekla, Öræfajökull and other volcanoes in Iceland","authors":"P. Einarsson","doi":"10.33799/jokull2019.69.035","DOIUrl":"https://doi.org/10.33799/jokull2019.69.035","url":null,"abstract":"Detecting unusual activity leading to the outbreak of a volcanic eruption is of vital importance for the short-term warning to the local population of an impending eruption. The varied volcano types of Iceland and range of ambient conditions at which eruptions occur offer an unusually wide spectrum of volcanic phenomena and volcanic hazards during the initial phase of eruptions. A recent study of eruptions in Iceland during the last four decades of instrumental observations has revealed that all the eruptions had a detectable precursory seismic activity, that under favourable conditions can be used to issue short-term warnings to the surrounding communities. Considerable documentary data also exist for pre-instrumental times extending several centuries back in time, that can be compared to the instrumental experience. This is true in particular for two of the most active volcanoes, Katla and Hekla, that are sufficiently close to the populated areas of the country. All seven confirmed eruptions of Katla since 1625 were preceded by felt earthquakes, beginning one to nine hours before the eruption was detected and two to over twelve hours before a jökulhlaup from this partly sub-glacial volcano reached the inhabited areas. The behaviour of Hekla is quite different. Large eruptions from the main edifice of Hekla since 1510 were generally accompanied by rather weak seismic activity. Earthquakes are usually felt only minutes before the first explosion occurs, in the 1947 case even several minutes after the first explosion of the volcano. Eruptions of the Hekla volcanic system outside the main edifice are, on the other hand, accompanied by considerable seismic activity, and the precursor times may be more than three hours, even much longer. The two historical eruptions of Öræfajökull, in 1362 and 1727, were apparently preceded by felt seismicity, sufficient to alarm the local population.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"5 1","pages":"35-52"},"PeriodicalIF":0.9,"publicationDate":"2020-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79392360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Perennial snow patch detection based on remote sensing data on Tröllaskagi Peninsula, northern Iceland 冰岛北部Tröllaskagi半岛常年积雪的遥感探测

IF 0.9 4区地球科学

Jokull Pub Date : 2020-02-01 DOI: 10.33799/jokull2019.69.103

Hannah Tussetschläger, S. Brynjólfsson, S. Brynjólfsson, T. Nagler, R. Sailer, J. Stötter, J. Wuite

引用次数: 2

Mid-crustal storage and crystallization of Eyjafjallajökull ankaramites, South Iceland 冰岛南部Eyjafjallajökull ankaramite的中地壳储存与结晶

IF 0.9 4区地球科学

Jokull Pub Date : 2020-02-01 DOI: 10.33799/jokull2019.69.083

P. Nikkola, E. Bali, M. Kahl, Q. V. D. van der Meer, O. T. Rämö, G. Guðfinnsson, T. Thordarson

{"title":"Mid-crustal storage and crystallization of Eyjafjallajökull ankaramites, South Iceland","authors":"P. Nikkola, E. Bali, M. Kahl, Q. V. D. van der Meer, O. T. Rämö, G. Guðfinnsson, T. Thordarson","doi":"10.33799/jokull2019.69.083","DOIUrl":"https://doi.org/10.33799/jokull2019.69.083","url":null,"abstract":"Our understanding of the long-term intrusive and eruptive behaviour of volcanic systems is hampered by a relatively short period of direct observation. To probe the conditions of crustal magma storage below South Iceland, we have analysed compositions of minerals, mineral zoning patterns, and melt inclusions from two Eyjafjallajökull ankaramites located at Brattaskjól and Hvammsmúli. These two units are rich in compositionally diverse macrocrysts, including the most magnesian olivine (Fo88−90) and clinopyroxene (Mg#cpx 89.8) known from Eyjafjallajökull. Olivine-hosted spinel inclusions have high Cr#spl (52–80) and TiO2 (1–3 wt%) and low Al2O3 (8–22 wt%) compared to typical Icelandic chromian spinel. The spinel-olivine oxybarometer implies a moderate oxygen fugacity of ∆logFMQ 0–0.5 at the time of crystallization, and clinopyroxene-liquid thermobarometry crystallization at mid-crustal pressures (1.7–4.2 kbar, 3.0±1.4 kbar on average) at 1120– 1195◦C. Liquid-only thermometry for melt inclusions with Mg#melt 56.1–68.5 and olivine-liquid thermometry for olivine macrocrysts with Fo80.7−88.9 yield crystallization temperatures of 1155–1222◦C and 1136–1213◦C, respectively. Diffusion modelling of compositional zonations in the Brattaskjól olivine grains imply that the Brattaskjól macrocrysts were mobilized and transported to the surface from their mid-crustal storage within a few weeks (at most in 9–37 days). Trends in clinopyroxene macrocryst compositions and the scarcity of plagioclase indicate that the mid-crustal cotectic assemblage was olivine and clinopyroxene, with plagioclase joining the fractionating mineral assemblage later. In all, the crystal cargoes in the Brattaskjól and Hvammsmúli ankaramites are composed of agitated wehrlitic or plagioclase wehrlitic crystal mushes that crystallized over a large temperature interval at mid-crustal depths.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"8 1","pages":"83-102"},"PeriodicalIF":0.9,"publicationDate":"2020-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82507235","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5

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