Laserfiche WebLink
• Surface extent of landslide movements. <br />. • Depth of landslide. <br />• Nature of landslide materials. <br />• Evidence of current instability. <br />• Nature of lineaments. <br />Surface Extent of Landslide Movements <br />Figure 1 is a plan which shows the limits of landslide movements and landslide deposits on the <br />„ - -north Slope of Jumbo Mountain, based on surface observations, air photo interpretation, and <br />- interpretation of drilling results. <br />Landslide deposits exceeding 100 feet in thickness were penetrated by borings ]orated through <br />a bench or terrace which occupies a zone up to 2,000 feet wide between the 6,620-foot and <br />6,850-foot contours (Figure 1). These landslide deposits aze underlain by the lower part of the <br />'B' seam suggesting that a bedding plane or parting in this seam formed the base of major slide <br />movements. The 'B' seam outcrop, therefore, represents the downslope limit of landslide <br />deposits. These deposits clearly represent the remnant of a lazge ancient landslide. Much of <br />• the original landslide deposit has been removed and reshaped by erosion and consolidation. This <br />is the reason that the surface of the landslide deposit no longer conforms to a normal landslide <br />configuration and exhibits no evidence of surface movement. <br />Because of the age of this landslide and the subsequent geomorphic and erosional history, it is <br />not possible to determine the upslope or southern boundary of movement. Two prominent <br />scarps shown on Figure 1 may represent the back of the original slide. These scarps expose in <br />situ strata and, therefore, indicate that movements did not extend any further upslope. The east <br />and west boundaries aze also based partly on observations of in situ outcropping strata. Overall, <br />the limits of the old landslide shown on Figure 1 should be considered as the outermost <br />boundary within which sliding occurred. <br />Depth of Landslide <br />Figure 2 shows the locations of cross-sections through the old landslide. Figures 3 through 5 <br />aze north-south cross-sections. Figure 6 shows structure contours on the top of bedrock or base <br />of the slide as interpreted from the boring logs. Figure 7 shows isopachs of the landslide <br />thickness based on the same data. <br />• <br />-2- <br />0: \Off\30\JPTURCO•RpC. Lkl <br />