Lineament control on drainage basin development, large rock landslides and mountain slope deformation in the southwest coast mountains, British Columbia, Canada

• Main Author: English, Russell Richard
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/8077

This research describes lineaments in the southwestern Coast mountains of British Columbia and their effect on landscape evolution and contemporary geomorphic processes. Lineaments mapped on air photographs are reflective of bedrock structure. Three regional trends are evidenced: a Cretaceous, northwest trend; a Tertiary norhteast trend; and an east-west trend which may represent recent crustal convergence between the North American and Juan de Fuca plates. Field and air photo evidence suggests lineaments should be interpreted primarily as either faults or large-scale regional joints. Lineament control of basin axial position is demonstrated. The spatial correlation between stream segments and lineaments is determined using the IDRISI GIS. On average 66% of the stream network overlies lineaments and 51% of lineaments in a basin are overlain by streams. The relationship of lineament length to basin morphometry is assessed by linear regression and compared to the relation between stream length and basin morphometry, Stream length is a better predictor of basin morphometry but lineament length is a good predictor of many parameters and becomes more important as basin area increases. It is speculated that lineaments become more important than streams in determining mean topography as landscape scale increases. 20 sites of large rock landslides and mountain slope deformation are identified in the study area. Rock avalanches and mountain slope deformation are the most common features, other failure types include rockfalls and landslides in surficial materials adjacent to rivers. Lineaments influence these features in three ways: 1) forming landslide headscarps; 2) providing locations about which slope deformation occurs; 3) forming rockfaces capable of shedding large rockfalls. Debris flow and avalanche initiation points are examined in the Seymour watershed north of Vancouver, British Columbia. These are almost twice as likely to occur where streams and lineaments intersect as where a stream only is present. This study suggests that the morphometry of drainage basins in the southwest Coast Mountains and some of the processes operating within them are a consequence of the underlying, tectonically emplaced bedrock structure. It is argued that processes operating at tectonic scales influence, and are reflected in, the landscape patterns around us.