Morphological Interpretations of Glacial Forms by Spatial Analysis in the Area Surrounding Lake Simcoe, Ontario
Publication: Cartographica: The International Journal for Geographic Information and Geovisualization
Volume 50, Number 3
ABSTRACT
ABSTRACT
Drumlins are sedimentary geological features that indicate the final direction of glacier movement; as a result, they are of great interest in understanding past glacial events. In southern Ontario alone, thousands of drumlins have been mapped and interpreted remotely through the use of aerial imagery or topographic maps. These are often paired with digital elevation models (DEMs) and/or contour maps offering detailed information about the area of study. This paper presents the results of a change-detection study that used maps of different vintages of the drumlin-rich area around Lake Simcoe in southern Ontario. Two topographic maps and two DEMs, each with contours at 25-ft (7.6-m) and 10-m intervals, were compared in three regions: (A) the urban region in the city of Orillia, overlying sand plains; (B) the area east of Orillia, on top of clay plains; and (C) the region south-east of Lake Simcoe, overlying till plains. The 7.6-m contour topographic maps and DEMs display comparable levels of detail; however, over time the drumlins appear to erode, likely a product of the underlying sediment in combination with urbanization. The 10-m contour topographic maps display less detail than DEMs of the same resolution, suggesting that the popular topographic maps are not the most reliable method of mapping drumlins.
RÉSUMÉ
Les drumlins sont des caractéristiques géologiques sédimentaires indiquant l'orientation finale du mouvement d'un glacier; par conséquent, ils présentent un grand intérêt pour comprendre les événements glaciaires du passé. Dans le Sud de l'Ontario seulement, des milliers de drumlins ont été cartographiés et télé-interprétés à l'aide de l'imagerie aérienne ou de cartes topographiques. Ces instruments sont souvent jumelés à des modèles altimétriques numériques (MAN) ou à des cartes en courbes de niveau offrant des renseignements détaillés sur la zone d'étude. L'auteur présente les résultats d'une étude de détection du changement faisant appel à des cartes de diverses époques de la zone riche en drumlins autour du lac Simcoe dans le Sud de l'Ontario. Deux cartes topographiques et deux MAN, chacun avec des courbes de niveau à 25 pi (7,6 m) et des intervalles de 10 mètres ont été comparées dans trois régions : A) région urbaine dans la ville d'Orillia, surplombant des deltas d'eskers; B) la zone à l'est d'Orillia, surplombant des plaines argileuses et C) la région au sud-est du lac Simcoe, surplombant des plaines de till. Les cartes topographiques à courbes de niveau de 25 pi (7,8 m) et les MAN affichent des niveaux de détail comparables; toutefois, au fil du temps, les drumlins semblent s'éroder, probablement en raison des sédiments sous-jacents, combinés à l'urbanisation. Les cartes topographiques à courbes de niveau de 10 m comportent moins de détails que les MAN offrant la même définition, ce qui laisse penser que les cartes topographiques populaires ne sont pas la méthode la plus fiable pour cartographier les drumlins.
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Information & Authors
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Published In
Cartographica: The International Journal for Geographic Information and Geovisualization
Volume 50 • Number 3 • Fall 2015
Pages: 165 - 171
Copyright
© University of Toronto Press 2015.
History
Published in print: Fall 2015
Published online: 8 September 2015
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Cartographica 2015 50:3, 165-171
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