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University of Helsinki Department of Geography
 
Department of Geography
Welcome
About

Jan Hjort, PhD

University lecturer / 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

 

 

Education

Ph.D., Department of Geography, University of Helsinki, 2006

Research interests

  • Modelling periglacial landforms and processes
  • Periglacial morphology
  • Geomorphological mapping
  • Geomorphology
  • Finland , Lapland

Current research: Spatial modelling of periglacial landforms and processes in subarctic landscapes

The current research is closely related to the topics of the doctoral thesis. The objectives are to (1) develop and test quantitative approaches to map periglacial processes in northern Finland, (2) compare statistical methods and spatial resolutions, (3) identify the environmental factors of the cryogenic processes (Figure 1) and (4) observe critical methodological shortcomings.

Figure 1. Periglacial patterned ground in Báišduattar – Áilegas fell area. Sorted polygons are ca. one metre in diameter (left photo). Sorted stone stripes are from 0.5 to 1.5 m wide and some tens of metres long. The photographs were taken by Jan Hjort in the summer 2002.

Doctoral thesis: Environmental factors affecting the occurrence of periglacial landforms in Finnish Lapland: a numerical approach (abstract) http://ethesis.helsinki.fi/julkaisut/mat/maant/vk/hjort/

The conclusions about the determinants of earth surface processes and landform patterns are often derived from traditional field survey methods. Recent developments in the spatial and numerical analysing techniques have improved the possibility to study different aspects of geomorphological phenomena in extensive regions. The objective of this research was to map and quantitatively analyse the occurrence of cryogenic phenomena in subarctic Finland in the zone of discontinuous permafrost. More precisely, utilising a grid-based approach the distribution and abundance of periglacial landforms were modelled to identify important landscape scale environmental factors and potential methodological limitations.

The study was performed using a comprehensive empirical data set of periglacial landforms from an area of 600 km2 at a 25-ha resolution. The utilised statistical methods were generalized linear modelling (GLM) and hierarchical partitioning (HP). GLMs were used to produce distribution and abundance models and HP to reveal independently the most likely causal variables. The GLM models were assessed utilising statistical evaluation measures, prediction maps, field observations and the results of HP analyses.

A total of 40 different landform types and subtypes were identified. At lower altitudes with gentle slope angles occurred earth hummock, stone pit, peat pounu and palsa continuums and at higher altitudes with steeper slopes sorted stripe, solifluction stream and solifluction sheet sequences were prevalent. At present, the environmental conditions promote the formation of different cryoturbation and peat accumulation based non-sorted features, whereas most of the sorted landforms were probably formed before the climatic optimum over 8000 years ago.

Topographical, soil property and vegetation variables were the primary correlates for the occurrence and cover of active periglacial landforms on the landscape scale. From the pure topographical factors, mean slope angle and mean altitude were commonly in the final models. Peat cover was the most important soil type variable because of its varying thermal properties and moisture holding capacity. Topographical wetness index was a crucial surrogate of environmental factor exhibiting the general soil moisture distribution. From vegetation variables, the shrub cover affected the distribution of several periglacial landforms.

In the model evaluation, most of the GLMs were shown to be robust although the explanation power, prediction ability as well as the selected explanatory variables varied between the models. The most robust distribution models were constructed with palsa, earth hummock, peat pounu, sorted solifluction sheet and sorted solifluction stream data. Earth hummock and peat pounu models obtained the best prediction and explanation ability in the abundance modelling, respectively.

The great potential of the combination of a spatial grid system, terrain data and novel statistical techniques to map the occurrence of periglacial landforms was demonstrated in this study. GLM proved to be a useful modelling framework for testing the shapes of the response functions and significances of the variables describing environmental gradients and the HP method helped to make better deductions of the important factors of earth surface processes. Hence, the numerical approach presented in this study can be a useful addition to the current range of techniques available to researchers to map and monitor different geographical phenomena. However, the data related limitations and method-based weaknesses may bias the modelling results and the model outcomes should not be interpreted uncritically.

Publications

Luoto, Miska & Jan Hjort (submitted). Downscaling coarse-grained geomorphological data to a finer spatial resolution. Earth Surface Processes and Landforms.

Hjort, Jan, Luoto, Miska & Matti Seppälä (In press). Landscape scale determinants of periglacial features in subarctic Finland: a grid-based modelling approach. Permafrost and Periglacial Processes.

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

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

Hjort, Jan & Miska Luoto (2006). Modelling patterned ground distribution in Finnish Lapland: an integration of topographical, ground and remote sensing information. Geografiska Annaler 88A: 1, 19–29.

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

Hjort, Jan & Miska Luoto (2005). Environmental determinants of earth hummock occurrence in Finnish Lapland: a case study based on generalized linear modelling (GLM) and hierarchical partitioning (HP). In Kumke, T. (ed.). Terra Nostra. 2 nd European Conference on Permafrost, June 12 – June 16, 2005, Potsdam, Germany, 65.

Hjort, Jan & Katariina Kosonen (2005; eds.). Palsoista Pajalaan. Tutkimusretki Pohjois-Fennoskandiassa. Helsingin yliopiston maantieteen laitoksen tutkimusretkiraportteja 41, Yliopistopaino, Helsinki. 137 pp.

Luoto, Miska & Jan Hjort (2004). Generalized linear modelling in periglacial studies: terrain parameters and patterned ground. Permafrost and periglacial processes 15: 4, 327–338.

Hjort, Jan (2003). Geographic information systems and remote sensing in the study of periglacial phenomena (in Finnish). Terra 115: 3, 209–215.

Hjort Jan & Matti 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, 63–64.

Hjort, Jan (2002). MapInfo software and landform mapping in geomorphological mapping of Syöte. In Kontturi, O. (ed.). Geoinformatical Methods in Geomorphological and Landscape Ecological Planning on County and Local Level, 24–27. Technical Services Centre, Pori.

Hjort, Jan (2001). Geomorphology of Syöte Life -area (in Finnish). In Lehtonen, Hannu (ed.). Luontoa ja historiaa Syötteen alueelta – Syöte Life-projektin perusselvitykset, 11–27. Metsähallitus, Oulu.

jort, Jan (2000). Climate change and its effect in Arctic regions (in Finnish). Terra 112: 3, 192–198.