Mapping Glaciers Over the Years

East African glaciers have been documented through various means since as early as the late 1800s. The evolution of modelling techniques has been key to gaining a better understanding of the changes they have been and are undergoing, as well as their underlying mechanisms.

Early Documentation

Initially, these observations were of a qualitative nature as they were side products of climbing, exploratory expeditions (Kaser, 2005). Hence, these mostly consisted of sketches, reports and photographs which illustrated the state of East African glaciers at the time (Messerli, 1980).  

Amongst these, some of the first and more detailed observations of Kilimanjaro's glaciers date back to the 1880s and are credited to Hans Meyer, a German geographer (Cullen, 2013). He recorded details of his ascent to the summit of Kilimanjaro in this report. 

Hans Meyer, Map of Kilimanjaro, Kibo Crater (1891) 

This map he drew up in 1891, based on his expedition, indicates evidence of an ice stream flowing over the crater rim, which he provided details about in his written report, eventually coming to be referred to as the Furtwangler glacier (Cullen, 2013).

Digital Mapping 

Eventually, as technology advanced, the modelling of East African glaciers moved on from mostly ground-base observations and terrestrial photogrammetry used primarily in the early to mid 20th century by Jaeger, 1909 and Klute, 1914, amongst others (Cullen, 2013). Although mid-century photography has been cited as being more reliable than written reports from the time, which often contained factual errors (Young, 1980), the later development of remote sensing techniques has allowed for much more precise mapping (Cullen, 2013). Specifically, these techniques consisted of aerial photography and satellite imagery which greatly developed and improved the accuracy of quantitatively mapping surface features in the late 20th and early 21st century (Karpillo, 2009). 

 

Satellite mapping in the late 1980s 

There are multiple steps in these processes, which include image acquisition, scanning and georeferencing, and, finally, the digitizing of glacier area (Karpillo, 2009). However, the specificity of these methods means that they require expert personnel, training and expensive equipment and thus rely on large capital investment. 

More recent aerial photography modelling study on Kilimanjaro, depicting the thinning of ice fields at the summit

 

There are also limitations to the extent of accuracy they allow for in mapping. For example, shadowed parts can obscure glacial margins, which can make it difficult to discern glacial boundaries, and glaciers covered by debris can be mistaken as surrounding terrain (Karpillo, 2009). 

A specific example of this was when glacial retreat in the Rwenzori range was mapped using Landsat satellite images during the period 1987-2003 (Klein, 2007). This led to important findings producing a continuous report of the loss of Rwenzori glacier mass since almost two decades ago. Nonetheless, the lack of cloud-free images made the interpretations more difficult, as well as the considerable snow cover on the edges of the glaciers in the two years of the study (1995 and 2003) which impeded the quantification of the glacier extent. 

Landsat images of the Rwenzori Range over the years 1987 - 2003

Moving Forward

Remote sensing is consistently being developed as a method given that it is capable of directly measuring multiple parameters of glaciers and the changes they experience (Raup, 2014). This constant development has yielded new insight into the most accurate detection of changes, including the measurement of the gravitational field through the Gravity, Recovery, and Climate Experiment (GRACE) satellite system, which determines changes below the orbit track. These Gravimetric satellites can lead to more robust and complete glacier assessments.