Jokull最新文献

{"title":"Geomorphologic evidence of jökulhlaups along the Hvítá River, southwestern Iceland","authors":"G. Wells, A. Dugmore, Þ. Sæmundsson, T. Beach, Sheryl Luzzadder-Beach, Daniel Ben‐Yehoshua","doi":"10.33799/jokull2022.72.035","DOIUrl":"https://doi.org/10.33799/jokull2022.72.035","url":null,"abstract":"Glacial outburst floods (jökulhlaups) have been a significant driver of landscape evolution, environmental change, and geohazards throughout the Quaternary. Iceland experiences more frequent jökulhlaups than nearly anywhere else on Earth, though most research focuses on subglacial volcanogenic floods that drain across outwash plains. Abundant geomorphologic evidence exists for largescale jökulhlaups that drained along the modern-day course of the Hvítá River in southwestern Iceland during early Holocene deglaciation, originating from ice-dammed Glacial Lake Kjölur; yet only one previous publication has investigated these events. This study uses a combination of field mapping and remote sensing to identify new jökulhlaup geomorphologic evidence along the Hvítá River, including erosional landforms such as scoured bedrock, anastomosing channel networks, cataracts, and canyons, and depositional features such as boulder bars and channel infill. We synthesize new findings with previously reported work to: 1) present an updated geomorphologic map of Hvítá jökulhlaup evidence; 2) reconstruct flood drainage routes, landscape impact, hydrology, and relative chronology; and 3) hypothesize scenarios of ice margin position and glacial lake evolution. Interpreting flood landform assemblages reveals a more extensive geomorphologic record than previously reported, with a complex drainage pattern along four separate routes from two potentially different sources. Reconstructed peak flow discharges span four orders of magnitude from 10**2 to 10**5 m3s-1. Geomorphologic and paleohydraulic results introduce four hypothesized drainage scenarios, though absolute geochronology is necessary to determine whether multiple floods drained along each route. The Hvítá jökulhlaups yield insight into the timing and dynamics of the final phase of Icelandic Ice Sheet decay, advancing understanding of Iceland’s Pleistocene–Holocene transition, demonstrating the importance of high magnitude, low frequency floods in landscape evolution, and serving as an analogue to ice and meltwater response to past, present, and future climate warming in glaciated regions worldwide.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"41 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90896405","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}

{"title":"Continuous monitoring of ice dynamics in Iceland with Sentinel-1 satellite radar images","authors":"J. Wuite, Ludivine Libert, T. Nagler, T. Jóhannesson","doi":"10.33799/jokull2022.72.001","DOIUrl":"https://doi.org/10.33799/jokull2022.72.001","url":null,"abstract":"In recent years, satellite remote sensing has revolutionized observations of glacier dynamics enabling for the first time the generation of detailed ice-velocity fields at regular intervals for Icelandic glaciers. We generated dense time series of ice-velocity fields from 2014 to 2020 exploiting the continuous acquisition of Sentinel-1 SAR using the offset-tracking technique. The fastest ice flow, with velocities up to 400–800 metres per year, is observed in the middle and lower part of the main outlet glaciers of the ice caps that span a large elevation range in the areas of high precipitation in the South and Southeast of Iceland. Several outlet glaciers of Vatnajökull, such as Skeiðarárjökull and Breiðamerkurjökull, draining towards the South and Southeast, show high-ice-speed channels with pronounced shearing zones where the ice speed increases by an order of magnitude within a distance of only a few ice thicknesses. Velocities on the order of a few tens of metres per year, and up to 50–100 metres per year, are observed on the large surge-type outlet glaciers of N- and W-Vatnajökull and generally on glaciers in the central Icelandic highland and in the northern and western part of the country. Slow-moving ice is observed along the main ice divides and near the glacier margins. The velocity data set is affected by gaps due to decorrelation, particularly during summer, because of temporal variations in the radar-image texture. The ice-velocity fields derived in this study from Sentinel-1 data agree well with other data sets, although these are affected by a larger number of outliers and data gaps, particularly in the accumulation areas. The generated velocity time series can be used for monitoring long-term dynamic trends, seasonal variations and for studying glaciological events such as surges or jökulhlaups.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"26 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80156588","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}

{"title":"Volcanic tremor associated with the Surtsey eruption of 1963–1967","authors":"S. Sayyadi, M. Gudmundsson, P. Einarsson","doi":"10.33799/jokull2022.72.021","DOIUrl":"https://doi.org/10.33799/jokull2022.72.021","url":null,"abstract":"The formation of the island of Surtsey over 3.5 years, remains one of the best-documented volcanic, island-forming eruptions to date. The basaltic submarine volcanic activity was detected on November 14, 1963, where ocean depth was 130 m prior to the eruption at the southern end of the Vestmannaeyjar archipelago. The eruptions occurred in several phases involving explosive and effusive activity, including the initial submarine phase on November 12–13, 1963. Separate phases of subaerial volcanic activity occurred during November 14, 1963–January 1964, January–April 1964, April 1964–May 1965, May–October 1965, December 1965–August 1966, and August 1966–June 1967. Seismic data quality from this period is inferior compared to that of modern monitoring systems. Four permanent seismic stations were operated in Iceland at the time, whereof only two, located at 115 and 140 km distance, had the sensitivity to record tremor from Surtsey. Nevertheless, the scanned analog seismograms (http://seismis.hi.is/) show that the eruptive activity was accompanied by considerable seismic activity, both earthquakes, and volcanic tremor. Earthquakes were primarily associated with changes in vent location. Both spasmodic and harmonic tremor was identified, both with low (<3 Hz) and higher (3–5 Hz) characteristic frequencies. The results indicate a complicated relationship between tremor and magma flow rate or style of activity. During the explosive eruption, the highest magma flow rates occurred in the first 10–20 days, a period with little observed tremor. The highest tremor is observed in December 1963–March 1964, after the discharge rates had dropped substantially, and on a timescale of hours-to-days, no clear relationship between tremor and eruption style is observed. The same applies to the effusive activity, where no seismic tremor was observed during most of the effusive eruption of Surtungur, despite the fact that magma flow rates were ~3 times higher than during later phases where some tremor was observed. Keywords: Submarine volcanism, eruption precursors, volcanic tremor, precursory tremor, continuous uprush eruptions","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"8 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84569384","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}

{"title":"A national glacier inventory and variations in glacier extent in Iceland 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, I. Kaldal, T. Jóhannesson","doi":"10.33799/jokull2020.70.001","DOIUrl":"https://doi.org/10.33799/jokull2020.70.001","url":null,"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":"49 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2021-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88351120","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}

{"title":"Little Ice Age advance of Kvískerjajöklar, Öræfajökull, Iceland.\u0000A contribution to the assessment of glacier variations in Iceland\u0000since the late 18th century","authors":"Snaevarr Gudmundsson, H. Bjornsson","doi":"10.33799/JOKULL2020.70.073","DOIUrl":"https://doi.org/10.33799/JOKULL2020.70.073","url":null,"abstract":"We describe the changes of the Kvískerjajöklar outlet glaciers in SE Iceland (presently ranging 600–1600 m a.s.l.), from their Little Ice Age maximum (LIAmax) to the present. We assume that glacier extent of the late 19th century approximately describes LIAmax although the glaciers already reached their peak extent in the 18th century. The former glacier margins were delineated from moraines, historical descriptions, topographical maps, aerial and oblique photographs, Landsat images and a lidar DEM. Along the previous glacier margins, elevation differences with respect to the lidar DEM of 2011 were estimated and contour maps of the glacier drawn at selected dates, maintaining the shape of the glacier surface as available maps. During the period 1890 to 2011, the outlets lost -0.4 m a-1 water equivalent evenly distributed over their surface and their area was reduced by 37% (from 10 km2 to 6.4 km2, 0.03 km2 a-1, 0.43 km3 water equivalent in total, i.e. 0.003 km3 w.e. a-1).","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"70 1","pages":"73-85"},"PeriodicalIF":0.9,"publicationDate":"2021-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86292408","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}

{"title":"The analog seismogram archives of Iceland: Scanning and preservation for future research","authors":"P. Einarsson, S. Jakobsson","doi":"10.33799/JOKULL2020.70.057","DOIUrl":"https://doi.org/10.33799/JOKULL2020.70.057","url":null,"abstract":"The history of seismography in Iceland began in 1909 with the installation of one horizontal Mainka seismograph in Reykjavík. Following a period of intermittent operation, regular operation was initiated in 1925 with the establishment of the Icelandic Meteorological Office. The number of stations increased gradually over the following decades, and in the sixties, four stations were in operation. The number of permanent stations proliferated following the Heimaey eruption in 1973 and during most of the eighties the number of stations was 40–50. The first digital seismograph stations were installed in 1990 and the analog seismic network was gradually replaced by digital stations over the next two decades. Between 1910 and 1920 the number of seismograms grew to an estimated 300,000. A four-year project to make this record collection accessible on the internet has been initiated and funded. So far around 175,000 seismograms have been scanned and the results are available and free for download on the open website seismis.hi.is. The seismograms are scanned with a resolution of 300 dpi and presented on the website as jpg-, and png-file. The high-resolution files are on the order of 4–8 Mb each. Digitization of the seismic traces has not been attempted since most of the seismograms are from short-period instruments and the waveforms are already lost. In addition to numerous teleseismic body-wave-phases, the record collection contains primary data from various tectonic and magmatic events in Iceland during the last century. This includes eruptions of Hekla in 1947, 1970, 1980–81, 1991 and 2000, Surtsey in 1963–1967, Heimaey in 1973, Askja in 1961, Grímsvötn in 1934, 1983, 1998, and 2004, Gjálp in 1996, rifting episode at Krafla in 1975–1984, persistent seismic activity of the Bárðarbunga and Katla volcanoes, numerous suspected subglacial magmatic events, earthquake swarms on the Reykjanes Peninsula Oblique Rift and within the Tjörnes Fracture Zone, and earthquake sequences in the transform zones of South and North Iceland and adjacent segments of the Mid-Atlantic Ridge.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"56 1","pages":"57-72"},"PeriodicalIF":0.9,"publicationDate":"2021-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76195475","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}

{"title":"Grímsvötn 1919-2019: The legacy of Erik Ygberg and Hakon Wadell","authors":"E. Sturkell, M. Gudmundsson","doi":"10.33799/JOKULL2020.70.129","DOIUrl":"https://doi.org/10.33799/JOKULL2020.70.129","url":null,"abstract":"The first recorded visit to Grímsvötn occurred on the 31st of August 1919. Two Swedish geology students, Hakon Wadell and Erik Ygberg, stood on the edge of a hitherto unknown large caldera. This discovery was the most significant finding in the first west-to-east transect across Vatnajökull, starting at Síðujökull on the 27th of August. This was an expedition into the unknown, but a principal aim was nevertheless to find the source of the large jökulhlaups on Skeiðarársandur. They named the ice-filled caldera “Svíagígur”. Studies of written sources in the 1930s revealed that this place was indeed Grímsvötn, well known in the 17th and 18th centuries but the name and location had been forgotten in the 19th century. From Svíagígur they continued eastwards, descending down the crevassed Heinabergsjökull, reaching civilization in the morning the 6th. They announced the news that a huge volcano existed under Vatnajökull and this was the source of the jökulhlaups emerging from Skeiðarárjökull. Upon their return to Stockholm, they received a hero’s welcome, but soon it all changed into no one believing them, as prominent figures in Sweden at this time insisted that a volcano can’t be active beneath a glacier! After they finished their studies, both left Sweden very disappointed. Hakon Wadell had a successful geological career in America presenting a doctoral thesis in 1932 from the University of Chicago. Erik Ygberg worked as an international prospector a few years before his bad health, a result of the hardships experienced at the end of the Vatnajökull expedition, forced him back to Sweden, where he had a career at the Swedish Geological Survey. The name Svíagígur has not been used but the two nunataks marking the highest points on Grímsfjall are named in the honour of the two Swedes, Svíahúkur eystri and Svíahnúkur vestri.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"15 1","pages":"129-138"},"PeriodicalIF":0.9,"publicationDate":"2021-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78416273","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}

{"title":"Fostering glacier termini","authors":"H. Hannesdóttir, O. Sigurdsson, B. Einarsson, Snaevarr Gudmundsson","doi":"10.33799/JOKULL2020.70.087","DOIUrl":"https://doi.org/10.33799/JOKULL2020.70.087","url":null,"abstract":"The article presents an overview of the history of the monitoring programme of glacier termini fluctuations in Iceland. The programme was initiated by meteorologist Jón Eyþórsson in 1930, and the measurements\u0000were initially carried out by local farmers. In recent decades, the measurements have been conducted by volunteers of the Iceland Glaciological Society with a very diverse professional background. Every autumn, the distance to the glacier terminus has been measured from a reference post, usually marked with a cairn and/or a metal pole. Glacier terminus variations in Iceland since 1930 show a clear relationship with climate changes. The terminus variations data set also contains information about the surges of many glaciers.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"7 1","pages":"87-110"},"PeriodicalIF":0.9,"publicationDate":"2021-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81866732","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}

{"title":"Infinite Next: Grímsvötn caldera and planet Earth","authors":"Anna Líndal, Bjarki Bragason","doi":"10.33799/JOKULL2020.70.139","DOIUrl":"https://doi.org/10.33799/JOKULL2020.70.139","url":null,"abstract":"In this article artists Anna Líndal and Bjarki Bragason discuss their work Two thousand nineteen hundred and Nineteen. The work was presented during the Iceland Glaciological Society’s (IGS) work trip to the Grímsvötn caldera in Vatnajökull glacier on 31. August 2019 in commemoration of the 100th anniversary of Hakon Wadell’s and Erik Ygberg’s 1919 expedition to the area and its subsequent mapping. Anna Líndal’s photographic work, Untouched expanse in the opening of the article addresses the importance of observing and recognizing the significance of minor events within the larger context of the environment. The Grímsvötn caldera is in the work observed as a self contained system which, although remote and harsh to its visitors, the artist proposes that it mirrors changes in the world at large. Even though footsteps trodden in the area vanish and blend into the environment, the bodily pressure of one person’s foot creates an imprint which acts as a reflector for sunbeams as ash is moved from the surface of the ice, making it more susceptible to exposure and melting. In this way the environment is continuously altered by human activity despite its constant appearance as untouched wilderness. Their two-part work presented and donated to the IGS cabin at Grímsfjall, Líndal and Bragason aimed to underscore the collision of human and geological time scales which may be discerned through the recognition of the anniversary of human eyes first laying sight on the caldera and its emergence from being an idea in the world (for example in Peter Raben’s 1720 map of Iceland) to becoming a mapped site. One component of the work is a set of cake plates which display two maps of Vatnajökull glacier, on the top side Wadell and Ygberg’s 1919 expedition path is dotted (the first recorded West-East crossing of the glacier). The underside of the plate reveals a recent map of Vatnajökull and the many, though not finite, survey lines established there in recent years and decades. Before the 22 participants in the trip to Grímsvötn drove together from the IGS cabin to the edge of the caldera, to stand in what is believed to be the spot where Wadell and Ygberg put down their tent a century ago, cake with a sugar printed map of the 1919 journey was served on the plates. The second component of the artistic gesture made during the 2019 trip was a wish from the artists to the participants in the trip to walk in silence from where the cars were parked towards the edge of the caldera. Silence in this context served as a means for individual critical and poetic reflection, offering participants for a short moment the opportunity to experience on their own terms the significance of seeing the caldera unfold in front of them at this momentous point in the site’s history.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"25 1","pages":"139-144"},"PeriodicalIF":0.9,"publicationDate":"2021-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82504983","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}

{"title":"Glacier variations 1930-1970, 1970-1995, 1995-2018 and 2018-2019","authors":"H. Hannesdóttir","doi":"10.33799/JOKULL2020.70.111","DOIUrl":"https://doi.org/10.33799/JOKULL2020.70.111","url":null,"abstract":"The Icelandic Glaciological Society received reports on approximately 50 measurements sites of glacier front variations in the autumn of 2019. Glacier retreat was observed at 80% of survey sites whereas advances\u0000where reported from 4 sites. The warm summer led to fewer snow-covered glacier margins, and more successful surveys. As in recent years the proglacial lakes make terminus measurements more difficult, although\u0000the laser rangefinder works well.","PeriodicalId":56284,"journal":{"name":"Jokull","volume":"1 1","pages":"111-118"},"PeriodicalIF":0.9,"publicationDate":"2021-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90850717","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}