Langjökull, Þórisjökull, and Eiríksjökull

Glacial Area from September, 1994 to October, 1998

Christopher Allen
Advanced Image Processing—ES 775
Emporia State University
April 25, 2017

Introduction

This project aimed to investigate glaciers in the southern region of Iceland, namely to monitor how their overall area varied over a period of several years as well as determine what amount of their surface area was composed of ice and firn, or the previous season's unmelted snow. Three glaciers were studied: Langjökull, Þórisjökull (or Thórisjökul), and Eiríksjökull. Images used in this investigation are from Landsat 5 Thematic Mapper (TM) imagery, with before images from September 13, 1994 while after images are from October 1, 1998. These particular images were chosen due to the low number of clouds present as well as depicting the scene after summer melting but before fresh snowfall. Figure 1 shows a before/after comparison of these images, detailing the ice as a lilac color while firn is seen in areas of intense white.

1994
1998

Figure 1. False-color composite of Langjökull, Þórisjökull, Eiríksjökull, and their immediate surroundings.


Full Scene Analysis

False-color composites were generated from Landsat 5 TM bands 1, 4, and 3 for the blue, green, and red bands in order to differentiate between vegetation, bodies of water, and masses of ice in a near approximation of natural color. These bands were then fed into Idrisi Selva's Cluster module to identify areas of different ground cover, and then through the use of Reclass these different ground cover types were assigned as areas of ice, firn, and irrelevance. Figure 2 demonstrates a reclassified Cluster of the group of glaciers, with color palette adjusted through Adobe Photoshop to mimic the lilac and white of ice and firn, respectively.

1994 Cluster
1998 Cluster

Figure 2. Reclassified Cluster image of Langjökull, Þórisjökull, and Eiríksjökull. Areas of exposed ice are represented as purple, while firn is represented with white.

An area calculation was performed on the scene to determine that the glacier covered 966 km² in 1994 and shrunk to an area of 886 km² by 1998. Utilizing Cluster and Reclass modules allowed for the amount of ice and firn area to be determined during the two years, shown below in Table 1. Rounding accounts for totals not adding up between rows. Cluster analysis determined that the area of exposed ice across the three glaciers had increased from 1994 to 1998.

Table 1.
Year
Ice Area
Firn Area
Total Area
1994
439 km²
527 km²
966 km²
1998
561 km²
354 km²
886 km²


Analysis of Eiríksjökull

The same methods were then carried out for two subscenes of the overall scene, each showing one of the other two glaciers. Cluster analysis and reclassification were carried out on the same bands as previously done on the full scene to determine the surface coverage of ice and firn for these individual glaciers. Figure 3 shows a natural coflor comparison of Eiríksjökull in 1994 and 1998, followed immediately by Figure 4 which shows a reclassified Cluster of the same scene. Table 2 details the ice and firn coverage of the two years, as well as the overall size of the glacier. Between 1994 and 1998, Eiríksjökull saw a decrease in its size consistent with that of the scene as a whole, but the amount of firn actually increased between the years of interest while the ice area decreased.

1994
1998

Figure 3. Subscene of Eiríksjökull depicting its appearance in 1994 and 1998.



1994
1998

Figure 4. Reclassified Cluster image of Eiríksjökull. Areas of exposed
ice are represented as purple, while firn is represented with white.


Table 2.
Year
Ice Area
Firn Area
Total Area
1994
13 km²
12 km²
25 km²
1998
7 km²
15 km²
22 km²


Analysis of Þórisjökull

The same analysis was carried out on a subscene of Þórisjökull, isolating it from other features within the scene to run Cluster analysis on its surface area. Figure 5 shows a false color composite before/after comparison, and Figure 6 displays the generated Cluster images in a before/after composition. Table 3 details the change in ice area, firn area, and total area between 1994 and 1998. As with Eiríksjökull, this glacier saw a decrease in size from 1994 to 1998 while exhibiting the same changes in exposed ice area and firn area.

1994
1998

Figure 5. Subscene of Þórisjökull depicting its appearance in 1994 and 1998.



1994
1998

Figure 6. Reclassified Cluster image of Þórisjökull. Areas of exposed
ice are represented as purple, while firn is represented with white.


Table 3.
Year
Ice Area
Firn Area
Total Area
1994
17.5 km²
15.5 km²
33 km²
1998
5 km²
22 km²
28 km²


Conclusions

From 1994 to 1998, glaciers within this southern region of Iceland all exhibited shrinkage in total area. This much is evident in satellite imagery and can be quantitatively expressed. As a whole, the region saw a decrease in the amount of firn, snow from the previous year, alongside an increase in exposed ice. This is to be expected, as a glacier's size will decrease when there is not enough snow from the previous year remaining at the end of summer to make up for mass lost through seasonal melting. Surprisingly, this trend of increased ice and decreased firn was only observable on the largest glacier of the three, Langjökull. The neighboring glaciers Þórisjökull and Eiríksjökull themselves exhibited the reverse of the regional trend, which is to say that their exposed ice area decreased and their area of virn increased. This suggests that the much larger Langjökull is more susceptible to overall climatic changes for a reason which remains undetermined by this research.