Tuesday, May 10, 2011

Jackson County, North Carolina Real Estate: Landslides "Not Surprising"

Jackson County, NC Realtors Fail to Disclose Mountain Slope Landslide/Soil Hazards

Data from soil surveys and North Carolina geologists find that Jackson County, NC real estate and HOA private roads are subject to slope failures, debris flows and underground landslides. These  identifiable land impediments are not referenced on MLS listings, sales contracts and Subdivision Street Disclosure Statements.

Adverse building site conditions are material facts yet this information has not been forthcoming from Jackson County, NC Realtors. This omission is curious since the planning board stated in 2006 that approximately 50% of Jackson County land is unstable.

This recent North Carolina Geological Survey report details Jackson County, NC landslides:
Landslide Hazard Mapping Update
Jackson County Planning Board
April 14, 2011

A. Overview of work completed from 2/22/201 through 4/8/2011.

NCGS staff briefed Planning Board on 2/8/11. Field work began on 2/22/2011 and initially concentrated on sites identified by Robby Shelton. Field crews are now conducting routine mapping at various locations in the county several days a week.

Mapping Summary

Total Number of landslides documented in field: 40
Accompanied by Robby Shelton: 19
Field Crews Only: 21
Landslides on unmodified slopes 15
Landslides on modified slopes 25
Total field data collection locations: 231

B. Major issues.

No major issues with work progress have been identified to date. Given the extent of steep slopes in the County, the number of slope movements and slope movement deposits identified to date is not surprising.

C. Things anticipated/not anticipated.

An embankment failure/debris flow associated with acid-producing rock at the Mountain Heritage development is not unlike similar occurrences with acid-producing rock in Macon, Haywood and Swain Counties. As hoped, field crews have been able to confirm debris flow sites on the ground that were identified from 1953 aerial photography.

D. Information or assistance needed from Planning Board.

Cooperation and interest from County staff, especially Gerald Green, Robby Shelton and Kevin Jamison has greatly facilitated the project. Field guidance and historical information on landslides provided by Robby Shelton has been a great help in expediting the mapping and data collection. Thanks to Kevin Jamison who provided the new 2010 ortho-imagery on 4/11/2011. Identification of any areas of concern within the County will help prioritize sites for field visits.

Notes on Selected Sites Investigated to Date

Active, Slow-Moving Landslides

Sutton Road weathered-rock slide: Past slide movement affected outbuilding and driveway on upper slope. Continued movement could potentially affect homes at the toe of the slope.

Figure 1. Preliminary map showing the outline of the slow-moving landslide in weathered rock. The shaded area indicates the approximate outline of the slide as of April 2011. Blue dot is a mapping reference location near the upslope extent of the slide. 2010 orthophotograph map base.

Ramp Cove Debris Slide: Slide reactivated in 2007 after excavation in toe of older, dormant slide that had developed in a pre-existing debris deposit. A home site under construction was abandoned after slide movement covered part of the foundation excavation for a new house. Residences below toe of active slide currently not affected by slide activity.

Figure 2. Preliminary map showing a landslide developed in pre-existing debris deposits in Ramp Cove.The shaded area shows the approximate extent of the active slide as of March 2011. Ground rupture lines outside of the shaded area show the approximate locations of inactive scarps indicating the presence of a feature interpreted as an older, now dormant, debris slide also within pre-existing debris deposits. Yellow dots are mapping reference locations near the upslope extents of the slides. 2010 orthophotograph map base.


Green Gables Development: Cut slope failure in debris deposit affecting property, but not immediately threatening residence.


Tuckaway - U.S. 281 Debris Slide: Cracks observed in embankment of recent NCDOT road repair. Active slide mass below the highway appears to extend downslope to shoreline of Bear Lake. Slide movement appears to be affecting a vacation home.

Figure 3. Preliminary map of an active debris slide and other debris deposits along U.S. 281 near Tuckaway Road. Pink shaded area outlines the extent of the active slide as of April 2011. Orange shaded areas are debris deposits from previous slope movement events. Yellow dot is a mapping reference location near the upslope extent of theslide. 2010 orthophotograph map base.

Figure 4. Photograph of a scarp (ground rupture line) with vertical displacement) within the active area of the Tuckaway-U.S. 281 slide. Ground movement has split the tree straddling the scarp. Other leaning and curved trees in the area indicate slide movement.

Stillwell Branch (EBCI) Weathered-rock Slide: Initial mapping done of cut slope failure/weathered-rock slide above a house site. Additional field work needed to assess any potential hazard to residents.
Debris Flows, Debris Slides, Debris Deposits

Tilley Creek Debris Flow: 1973(?) debris flow that damaged cabin. The run out zone of the debris flow is on an older debris fan surface. The debris flow appears to have initiated on an unmodified (“natural”) slope.

Figure 5. Map showing the path or track (pink shaded area) of a 1973(?) debris flow that damaged a cabin near Tilley Creek Road. The cabin was abandoned after the debris flow event. The debris flow deposited material on pre-existing debris deposits from previous debris flow events. 2010 orthophotograph map base.

Kiesse Creek: Two embankment failures/debris flows during Frances-Ivan,  in September 2004 merged into one~4,000-foot long track that impacted Bear Lake Preserve property and contributed sediment to Bear Lake. Remaining embankment in vicinity of debris flow initiation zones remains unstable.

Sheep Cliff-Glenville: Embankment failure/debris flow during Frances-Ivan, in September 2004. Sedimentation in creek, homes not damaged or threatened. Some of remaining embankment material at the head of the debris flow is unstable.

Mountain. Heritage Development: 2009(?) embankment failure/debris flow, and cut slope failure/debris slide. Embankment failure/debris flow developed in embankment derived from sulfidic rock excavated from cut slope. Cut slope failure developed in colluvium.
Dark Road: Home damaged by a cut slope failure/debris slide. Home had to be repositioned onto foundation and is now in foreclosure.
Geologic Hazards

Pump Mountain Cut (U.S. 23/Hospital Road): Altered ulramafic(olivine) rock with asbestos minerals is exposed in cuts and other graded areas.  Our mapping program will likely result in some small adjustments to the outline of the ultramafic rock map unit into areas not previously mapped as ultramafic rock.  Two slope failures were identified: a small rock slide related to talc on planes of weakness in olivine rock (dunite); and a small embankment/sediment pond failure in micaceaous soil.  Impacts from the slope failures are on-site. Some additional mapping is planned for this area to evaluate extent of the ultramafic rock and asbestos minerals.

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