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University of Helsinki Department of Geography
 
Department of Geography
Welcome
About

Jan Hjort, PhD

Post Doctoral Researcher

Department of Geography
P.O. Box 64 (Gustaf Hällströmin katu 2)
00014 University of Helsinki
Finland

Tel: +358 (0)9 191 51067
Fax. +358 (0)9 191 50760
E-mail: jan.hjort@helsinki.fi

 

 

Degrees, diplomas and the equivalent

Docent in Physical Geography, Department of Geography, University of Helsinki, 2008

Doctor of Philosophy, Department of Geography, University of Helsinki, 2006 (Especially meritorious academic dissertation, University of Helsinki, 2007)

Master of Science, Department of Geography, University of Helsinki, 2001

Project work education, University of Helsinki, Finland, 1999

Research interests

  • Geomorphology, Biogeomorphology, Geodiversity
  • Statistical modelling, Spatial modelling
  • Periglacial processes and landforms
  • Finland, sub-Arctic and Arctic regions, Lapland

Current research projects:

Spatial modelling of periglacial processes under environmental change

Geomorphological systems of Arctic and sub-Arctic regions are sensitive to changes in environmental conditions. The potential consequences of global change on the earth surface processes are, however, inadequately explored. This research project aims to develop and test novel approaches to model the occurrences and distributional alterations of periglacial processes in response to climate change. The ultimate goal is to make a significant step forward in combining empirical, geographic information (GI) and remote sensing (RS) data to predict and analyze complex geomorphological processes at various spatial scales (Fig. 1).

This project focuses on four key issues in which further research on the spatial modelling of periglacial processes is especially needed:

(1) Compilation of causal environmental factors of periglacial processes.

(2) Comparison of different statistical techniques and downscaling methods in periglacial modelling.

(3) Estimation of potential effect of environmental change on the distribution of periglacial processes.

(4) Detection of critical methodological pitfals and evaluation of the extrapolation potential of the geomorphological distribution models.

The study sites are located in sub-Arctic Fennoscandia. The work utilizes high-quality empirical data sets of periglacial processes and landforms. The research includes extensive national and international collaboration with geomorphologists, spatial modellers and RS specialists. The results of the project will benefit the monitoring of cold climate environment by providing approaches to analyze periglacial processes, firstly in current environmental conditions and, secondly, in the context of global change.

 

 

Figure 1. A prediction map on the occurrence of solifluction (from yellow to red) and permafrost hummocks (palsas; blue) in the Paistunturit fell region, northernmost Finland. The darker the colour within a 1-ha grid square, the higher the probability of an occurrence of periglacial features. The vertical interval of the contours is 20 m.

 

Permafrost observatory in the Nordic Arctic: sensitivity and feedback mechanisms of permafrost changes

The project focuses on interactions between landscapes, climate and permafrost, which vary according to global environmental changes. Some of these changes will have important impacts for local and indigenous people's living conditions and economic and cultural development opportunities. Thus, improving the monitoring and understanding of the sensitivity and feedback mechanisms of permafrost is essential for most Nordic countries and will improve the understanding of unique Nordic Arctic aspects of permafrost with site specific variations and impacts for people.

The main objectives of this project are to:

(1) characterise the spatial variability of permafrost history and biogeochemical features within the upper 4-5 meters of the permafrost-active layer system across Nordic sites at different landscape types

(2) monitor active-layer temperature and depth and install permafrost temperature probes for improved understanding of thermal and nival offsets on the palsa landforms, which will be studied mainly at all three sites

(3) characterize permafrost layers in terms of sediment or bedrock type, element stocks, ice content and ages

(4) analyse the short and long-term potential and actual subsurface CO2, CH4 and N2O production in relation to permafrost degradation and the associated changes in availability of substrate, nutrients, water and oxygen.

 

PYRN-TSP - Permafrost Young Researchers Network’s Contribution to the Thermal State of Permafrost Project in the Nordic Countries

PYRN – TSP is a contribution to the International Polar Year (IPY) from a consortium of Nordic-based institutions which addresses the burning issue of impacts of increasing global temperatures on terrestrial permafrost. Recent major concerns about potential impacts of permafrost thawing on man-made infrastructure have prompted the launch of international projects aiming at creating a globally consistent approach to permafrost monitoring, but the current knowledge on the extent and the thermal conditions of permafrost in Scandinavia is scarce.

PYRN-TSP will provide young Nordic researchers with the means to conduct simple yet powerful measurements of permafrost conditions either in areas where records of prior observation exist (to establish recent trends) or in new undisturbed areas. The project will help to resolve the current issue on the thermal state of permafrost in the Nordic countries and provide other communities (e.g. modeling community, ecologists, engineers and others) within the IPY with data needed to predict future impacts of thawing permafrost so that adaptation strategies can be developed.

 

Selected publications in English

Hjort, J. & M. Luoto (2009; in press). Geodiversity of high-latitude landscapes in northern Finland. Geomorphology.

Luoto, M., Marmion, M. & J. Hjort (2009; in press). Assessing the spatial uncertainty in predictive geomorphological mapping: a multi-modelling approach. Computers and Geosciences.

Hjort, J. & M. Luoto (2009). Interaction of geomorphic and ecologic features across altitudinal zones in a subarctic landscape. Geomorphology, 112, 324–333.

Hjort, J. & M. Marmion (2009). Periglacial distribution modelling with a boosting method. Permafrost and Periglacial Processes 20, 15–25.

Marmion, M., Hjort, J., Thuiller, W. & M. Luoto (2009). Statistical consensus methods for improving predictive geomorphology maps. Computers and Geosciences 35, 615–625.

Hjort, J. & M. Marmion (2008). Effects of sample size on the accuracy of geomorphological models. Geomorphology 102, 341–350.

Marmion, M., Hjort, J., Thuiller, W. & M. Luoto (2008). A comparison of predictive methods in modelling the distribution of periglacial landforms in Finnish Lapland. Earth Surface Processes and Landforms 33, 2241–2254.

Hjort, J. & M. Luoto (2008) . Factors Controlling Periglacial Geodiversity in Subarctic Finland. In Kane, D. L. & K. M. Hinkel (eds.), Proceedings, Ninth International Conference on Permafrost 29 June–3 July 2008. Fairbanks, Alaska. University of Alaska, Fairbanks, 717–722.

Marmion, M., Luoto, M., Hjort, J. & M. Parviainen (2008) . New Insights into Spatial Uncertainty in Predictive Periglacial Modeling. In Kane, D. L. & K. M. Hinkel (eds.), Proceedings, Ninth International Conference on Permafrost 29 June–3 July 2008. Fairbanks, Alaska. University of Alaska, Fairbanks, 1137–1141.

Hjort, J. & M. Luoto (2008). Can abundance of geomorphological features be predicted using presence-absence data? Earth Surface Processes and Landforms 33, 741–750..

Luoto, M. & J. Hjort (2008). Downscaling of coarse-grained geomorphological data. Earth Surface Processes and Landforms 33, 75–89.

Hjort, J. , Luoto, M. & M. Seppälä (2007). Landscape scale determinants of periglacial features in subarctic Finland: a grid-based modelling approach. Permafrost and Periglacial Processes 18, 115–127.

Hjort, J. (2006). Environmental factors affecting the occurrence of periglacial landforms in Finnish Lapland: a numerical approach (PhD Thesis). Shaker Verlag, Aachen. 162 p.

Luoto, M. & J. Hjort (2006). Scale matters – a multi-resolution study of the determinants of patterned ground activity in subarctic Finland. Geomorphology 80, 282–294.

Hjort, J. & M. Luoto (2006). Modelling patterned ground distribution in Finnish Lapland: an integration of topographical, ground and remote sensing information. Geografiska Annaler 88A, 19–29.

Luoto, M. & J. Hjort (2005). Evaluation of current statistical approaches for predictive geomorphological mapping. Geomorphology 67, 299–315.

Luoto, M. & J. Hjort (2004). Generalized linear modelling in periglacial studies: terrain parameters and patterned ground. Permafrost and Periglacial Processes 15: 4, 327– 338.

Hjort, J. & M. Seppälä (2003). Topographical properties of active and inactive patterned grounds in Finnish Lapland. In: Haeberli, W. & D. Brandová (Eds.), ICOP 2003.Permafrost. Extended Abstracts on Current Research and Newly Available Information. Swets & Zeitlinger, Lisse, pp. 63–64.

 

Submitted

Christiansen, H.H., Etzelmüller, B., Isaksen, K., Juliussen, H., Farbrot, H., Humlum, O., Johansson, M., Ingeman-Nielsen, T., Kristensen, L., Hjort, J., Holmlund, P., Sannel, A.B.K., Sigsgaard, C., Åkerman, H.J., Foged, N., Blirka, L.H., Pernosky, M.A. & R. Ødegård. The Thermal State of Permafrost in the Nordic area during IPY 2007-2009. Permafrost and Periglacial Processes.

Hjort, J. & M. Luoto. New insights into geomorphic process-environment relationships using simulated response curves. Earth Surface Processes and Landforms.

Virtanen, R., Luoto, M., Rämä, T., Mikkola, K., Hjort, J., Grytnes, J.-A. & J. Birks. Recent vegetation changes in the high-latitude tree-line ecotone are controlled by geomorphological disturbance, productivity and diversity. Global Ecology and Biogeography.