Pub Date : 2021-04-08DOI: 10.33799/JOKULL2020.70.035
R. Vestergaard, Gro Birkefeldt Møller Pedersen, C. Tegner
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.
利用新的遥感数据、历史报告、岩石学和基于地球化学数据的黏度估算，阐明了1845-46年和1766-68年大喷发期间Hekla峰顶脊的熔岩侵位流线和喷口结构的变化。根据平面测量法，我们估计这些喷发的体积分别接近0.4公里和0.7公里。然而，与1947年至1948年的喷发记录相比，平面测量法似乎低估了40-60%的熔岩体积。因此，真正的体积更可能分别为0.5-0.6公里和1.0-1.2公里。估计1766-68年喷发的熔体粘度平均值为2.5×10 Pa s(喷发前)和2.5×10 Pa s(脱气)，1845-46年喷发的熔体粘度平均值为2.2×10 Pa s(喷发前)和1.9×10 Pa s(脱气)。喷发前的岩浆比脱气岩浆的流动性要高一个数量级。在1845-46年和1947-48年的喷发中，SiO2从58-57 wt%下降到55-54 wt%，这与Hekla火山喷发的传统模型一致，即Hekla火山是从一个巨大的层状岩浆房喷发出来的，顶部是最进化的(富含硅的)岩浆。相比之下，1766 - 1768年的熔岩流显示出更为复杂的SiO2趋势。1766年位于其南部的熔岩场SiO2值为54.9 ~ 56.5%，而1767年3月在Hekla脊NE端较年轻喷口喷发的Hringlandahraun熔岩流SiO2值更高，为57.8%。这表明层状岩浆房模型并不适用于Hekla火山喷发期间形成的所有熔岩流。
{"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}
Pub Date : 2020-12-15DOI: 10.33799/JOKULL2020.70.119
Snaevarr Gudmundsson, H. Björnsson
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 most infamous river and for travellers, cruising on horseback, the greatest obstacle to cross on the main road. The river began shaping its present channel 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 this 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 wide 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 coastal 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.
{"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}
H. Hannesdóttir, O. Sigurðsson, R. Þrastarson, S. Guðmundsson, J. M. Belart, F. Pálsson, E. Magnússon, S. Víkingsson, T. Jóhannesson
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.
{"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}
Pub Date : 2020-02-01DOI: 10.33799/jokull2019.69.137o
Snaevarr Gudmundsson, H. Björnsson
Rapid changes in landforms and hydrology now take place at the margins of glaciers in Iceland due to their fast retreat in response to warming climate. We describe examples from the margins of Breiðamerkurjökull and Hoffellsjökull from the years 2010–2019 with significant impact on the runoff of meltwater, the location of river courses, the formation of glacial lakes and jökulhlaups.
{"title":"Glacier changes by Breiðamerkurjökull and Hoffellsjökull in 2010–2019.","authors":"Snaevarr Gudmundsson, H. Björnsson","doi":"10.33799/jokull2019.69.137o","DOIUrl":"https://doi.org/10.33799/jokull2019.69.137o","url":null,"abstract":"Rapid changes in landforms and hydrology now take place at the margins\u0000of glaciers in Iceland due to their fast retreat in response to warming climate. We describe examples from the margins of Breiðamerkurjökull and Hoffellsjökull from the years 2010–2019 with significant impact on the runoff of meltwater, the location of river courses, the formation of glacial lakes and jökulhlaups.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"15 1","pages":"137-144"},"PeriodicalIF":0.9,"publicationDate":"2020-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75156175","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}
Pub Date : 2020-02-01DOI: 10.33799/jokull2019.69.001
S. Guðmundsson, H. Björnsson, F. Pálsson, E. Magnússon, Þ. Sæmundsson, T. Jóhannesson
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 if 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.
{"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}
Pub Date : 2020-02-01DOI: 10.33799/jokull2019.69.129o
H. Hannesdóttir
Glacier variations 1930–1970, 1970–1995, 1995–2017 and 2017–2018 The Icelandic Glaciological Society received reports on 46 measurements sites of glacier front variations in the autumn of 2018. Glacier retreat was observed at 33 survey sites whereas advances where reported from 5 sites, and 4 showed no signs of change. Snow covered glacier margins, bad weather or floating icebergs in the proglacial lakes prevented measurement at a few sites. One new site was added to the network, the western part of Þórisjökull.
{"title":"Glacier variations 1930–1970, 1970–1995, 1995–2017 and 2017–2018","authors":"H. Hannesdóttir","doi":"10.33799/jokull2019.69.129o","DOIUrl":"https://doi.org/10.33799/jokull2019.69.129o","url":null,"abstract":"Glacier variations 1930–1970, 1970–1995, 1995–2017 and 2017–2018\u0000The Icelandic Glaciological Society received reports on 46 measurements sites of glacier front variations in the autumn of 2018. Glacier retreat was observed at 33 survey sites whereas advances where reported from 5 sites, and 4 showed no signs of change. Snow covered glacier margins, bad weather or floating icebergs in the proglacial lakes prevented measurement\u0000at a few sites. One new site was added to the network, the western part of Þórisjökull.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"107 1","pages":"129-136"},"PeriodicalIF":0.9,"publicationDate":"2020-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87876722","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}
Pub Date : 2020-02-01DOI: 10.33799/jokull2019.69.157o
M. Gudmundsson, J. Hólmjárn
{"title":"A 25.6 m long firn core extracted from the Grímsvötn ice shelf\u0000in June 1993","authors":"M. Gudmundsson, J. Hólmjárn","doi":"10.33799/jokull2019.69.157o","DOIUrl":"https://doi.org/10.33799/jokull2019.69.157o","url":null,"abstract":"","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"124 1","pages":"157-159"},"PeriodicalIF":0.9,"publicationDate":"2020-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88095976","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}
Pub Date : 2020-02-01DOI: 10.33799/jokull2019.69.035
P. Einarsson
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.
{"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}
Pub Date : 2020-02-01DOI: 10.33799/jokull2019.69.103
Hannah Tussetschläger, S. Brynjólfsson, S. Brynjólfsson, T. Nagler, R. Sailer, J. Stötter, J. Wuite
Hannah Tussetschläger1,∗, Skafti Brynjólfsson, Sveinn Brynjólfsson, Thomas Nagler, Rudolf Sailer, Johann Stötter and Jan Wuite Institute of Geography, University of Innsbruck, Austria; Icelandic Institute of Natural History, 600 Akureyri, Iceland Icelandic Meteorological Office, 600 Akureyri, Iceland ENVEO Environmental Earth Observation, Austria ∗Correspondence: Hannah.Tussetschlaeger@uibk.ac.at
奥地利因斯布鲁克大学地理研究所Hannah Tussetschläger1，∗，Skafti Brynjólfsson, Sveinn Brynjólfsson, Thomas Nagler, Rudolf Sailer, Johann Stötter和Jan Wuite;冰岛自然历史研究所，600 Akureyri，冰岛冰岛气象局，600 Akureyri，冰岛ENVEO环境地球观测，奥地利*通信:Hannah.Tussetschlaeger@uibk.ac.at
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Pub Date : 2020-02-01DOI: 10.33799/jokull2019.69.083
P. Nikkola, E. Bali, M. Kahl, Q. V. D. van der Meer, O. T. Rämö, G. Guðfinnsson, T. Thordarson
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.
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