LANDSLIDE ANALYSIS 
AND SUSCEPTIBILITY MAPPING 
Thomas T. Alfoldi P.Eng. 
Canada Centre for Remote Sensing 
Energy, Mines and Resources Canada 
ABSTRACT 
The eastern portion of Ontario is extensively covered by 
a glacio/lacustrian deposit, popularly called "Leda" clay. 
This clay has the particular feature of being extremely sensitive 
to disturbance. A critical loss of strength results from re 
moulding, which phenomenon is manifest throughout the region as 
landslides. Airphoto interpretation proves to be the only 
practical and economical means of identifying existing landslides 
over a large area. 
By examining the nature of such landslides in both theory 
and ground observation, and subsequently developing an airphoto 
recognition pattern, it has been possible to do an inventory of 
landslides over eastern Ontario using existing aerial photog 
raphy. An attempt is also made to construct a list of those 
parameters which are recordable on remotely - sensed imagery 
and indicate susceptibility to slope failure. 
INTRODUCTION 
Landslides are a common feature in eastern Ontario. It is 
disturbing to note that this phenomenon occurs repeatedly in 
populated areas, yet the state of the art for landslide prediction 
is in its infancy still. Detailed soil mechanics investigations 
of landslides or landslide - prone slopes is the most exacting 
form of analysis, yet is is impractical and costly when large 
regions must be considered. 
Remote sensing proves to be the best method of studying the 
regional aspect of landsliding. The first obvious step in this 
problem is to construct an inventory of existing landslides, 
since a landslide density map is also a rough form of a land 
slide susceptibility map. Such an inventory is ideally done, 
using airphoto interpretation. Similarly, evaluating the 
susceptibility of earth slopes to sliding can be accomplished 
qualitatively using remote sensing methods to cover large areas.