Framrásir jökla í neðri hluta Borgarfjarðar á síðjökultíma (Bølling-Allerød): rannsóknir á jökulhöggun og myndun setlaga og landforma - verkefni lokið

Fréttatilkynning verkefnisstjóra

16.9.2020

Niðurstöður verkefnisins sýna að jökull, sem eitt sinn skreið niður Borgarfjörð, var mun virkari en áður var talið. Þetta má sjá í fyrrnefndum sjávarbökkum, þar sem greina má sjö mismunandi jökulgarða undir yngri setlögum (Mynd 1 og 2). Aldursgreiningar gefa til kynna að þessir jökulgarðar hafi myndast hver á eftir öðrum fyrir 13-11 þúsund árum (mynd 3). Má af því ætla að jöklar hafi verið mjög virkir á tímum afjöklunar. Verkefnið og niðurstöður þess sýna einnig hve fjölbreytt ferli setmyndunar og aflögunar geta verið við jökla sem ganga í sjó fram, og hvaða hlutverki þau gegna í myndun stórra jökulgarða.

English:

The main aim of this project was to reconstruct past glacier dynamics in the lower Borgarfjörður regions, West Iceland. This was done by documenting in detail the stratigraphy and deformation structures in the 6 km long Belgsholt-Melabakkar-Ásbakkar coastal cliffs. Also, other sections and landforms inside the coast were analysed. The results show that glaciers that once flowed southwards through the Borgarfjörður valley and fjord were much more dynamic that previously assumed. As an example, seven separate advances could be identified as buried moraines within the coastal cliff sections (Figures 1 and 2). Radiocarbon dating of these formations indicates that they formed between 13 and 11 thousand years ago (Fig. 3). The results of this project highlight the diversity of sedimentological and glacial deformation processes involved in the construction of large moraines at the margins of glaciers that terminate in the sea, and indicate that such glaciers were more dynamic during the deglaciation than previously thought. A list of project outputs is provided above.

Afurðir verkefnisins:

PhD thesis:

Sigfúsdóttir, Th. 2019. Past dynamics of a marine-terminating glacier in lower Borgarfjörður, west Iceland. LUNDQUA THESIS 87. 125 p.

Peer-reviewd publications:

Sigfúsdóttir, Th. and Benediktsson, Í.Ö. 2020. Refining the history of Younger Dryas and Early Holocene glacier advances in the Borgarfjörður region, western Iceland. Boreas 49, 296-314. https://doi.org/10.1111/bor.12424.

Sigfúsdóttir, Th., Phillips, E., Benediktsson, Í.Ö. 2020. Micromorphological evidence for the role of pressurized water in the formation of large-scale thrust-block moraines in Melasveit, western Iceland. Quaternary Research 93, 88-109. https://doi.org/10.1017/qua.2019.48.

Sigfúsdóttir, Th., Benediktsson, Í.Ö., Phillips, E.R. 2018. Active retreat of a Late Weichselian marine-terminating glacier: An example from Melasveit, W-Iceland. Boreas 47, 813-836. https://doi.org/10.1111/bor.12306.

Conference abstracts (talks* and posters):

*Sigfúsdóttir, Th., Benediktsson, Í.Ö., Phillips, E. 2019. Past dynamics of a marineterminating

glacier in Borgarfjörður, west Iceland. Nordic Branch Meeting of the International Glaciological Society, Reykholt, Iceland, Oct 30- Nov 1 2019.

Sigfúsdóttir, Th., Phillips, E., Benediktsson, Í.Ö. 2019. The role of pressurised water in glaciotectonic thrusting. INQUA, Dublin, Ireland, 25th-31st July 2019.

*Sigfúsdóttir, Th., Benediktsson, Í.Ö., Phillips, E. 2018. Active retreat of a marineterminating glacier: Evidence from Late Weichselian sediments and glaciotectonics in western Iceland. 6th International Conference on ‘Palaeo-Arctic Spatial and Temporal (PAST) Gateways. Durham University, 16-20 April 2018.

*Sigfúsdóttir, Th., Benediktsson, Í.Ö., Phillips, E. 2018. Endurteknar framrásir jökuls í Melasveit í neðri hluta Borgarfjarðar á síðjökultíma. Vorráðstefna Jarðfræðafélags Íslands, Reykjavík, 9. mars 2018.

*Sigfúsdóttir, Th., Benediktsson, Í.Ö., Phillips, E. 2018. Active retreat of a Late Weichselian marine-terminating glacier revealed by large-scale glaciotectonics in Melasveit, western Iceland. The 33rd Nordic Geological Winter Meeting, 10-12 January, Kgs. Lyngby, Denmark.

*Sigfúsdóttir, Th., Benediktsson, Í.Ö., Phillips, E. 2016. Different styles of glaciotectonism during a retreat of a marine terminating glacier – examples from Iceland. 32nd Nordic Geological Winter Meeting, Helsinki, 13-15 January 2016.

Sigfúsdóttir, Th., Benediktsson, Í.Ö., Phillips, E. 2015. Late Weichselian glacier dynamics after ice-shelf collapse: analysis of glaciotectonics in lower Borgarfjörður, W-Iceland. EGU General Assembly 12-17 April, Vienna, Austria.

Sigfúsdóttir, Þ., Benediktsson, Í.Ö., Phillips, E.R. 2014. Bölling-Alleröd glacier dynamics in lower Borgarfjörður, western Iceland: multiple scale and multi-proxy analysis of glaciotectonics. Nordic Geological Winter Meeting, Lund, Sweden, January 8-10.

Popular science and consultancy:

- Þorbjörg Sigfúsdóttir og Ívar Örn Benediktsson (2021). Saga jökulframrása í neðra hluta Borgarfjarðar. Boð um grein í Borgfirðingabók 2021.

- Ívar Örn Benediktsson og Þorbjörg Sigfúsdóttir 2020. Saga jökulframrása og umhverfisbreytinga í neðra hluta Borgarfjarðar. Fræðsluerindi, Safnahús Borgarfjarðar, 10.9.2020.

- Some consultancy for the Hvalfjarðarsveit municipality in association with regional planning.

Fig 1. / Mynd 1. A model showing the formation of moraines by advances of the Borgarfjörður glacier between 13 and 11 thousand years ago. These moraines are now visible in the Belgsholt-MelabakkarÁsbakkar coastal cliffs. From Sigfúsdóttir et al. 2018. / Líkan að myndun jökulgarða í Melasveit við framrásir Borgarfjarðarjökuls fyrir 13-11 þús. árum síðan. Þessir jökulgarðar eru að mestu grafnir undir yngri setlögum en má greina í Belgsholtsbökkum, Melabökkum og Ásbökkum. Mynd frá Þorbjörgu Sigfúsdóttir o.fl. 2018.

Heiti verkefnis: Framrásir jökla í neðri hluta Borgarfjarðar á síðjökultíma (Bølling-Allerød): rannsóknir á jökulhöggun og myndun setlaga og landforma/Bølling-Allerød glacier dynamics in lower Borgarfjörður, Western Iceland: multiple-scale and multi-proxy analysis of glaciotectonics
Verkefnisstjóri: Ívar Örn Benediktsson, Raunvísindastofnun
Tegund styrks: Verkefnisstyrkur
Styrktímabil: 2014-2016
Fjárhæð styrks: 10,09 millj. kr. alls
Tilvísunarnúmer Rannís: 141002