A Deep-seated Gravitational Slope Deformation in the northern Monashee Complex, Monashee Mountains, British

Columbia, Canada

Danilo MorettiEarth Science Department

University of BolognaVisiting Student

Presentation Outline

• Introduction:– What is a deep-seated gravitational slope deformation?– Methods of studying DsGSD– Different approaches to and representations of DsGSD

• Objectives for this study• Field site description• Methodology• Timeline

DsGSD: huge gravitational phenomena affecting mountain slopes

Several phenomena indicated by literature with different names:

• Area extent “Large landslides”: Stini, 1952

• Thickness of the involved slope portion “Deep seated gravitational deformations”: Jahn, 1964

“Deep-reaching gravitational deformations”: Neemcock, 1972

• Time-interval of activity “Long term gravitational deformations”: Ghigira, 1992

• The alleged causes “Gravity tectonic phenomena”: Engelen, 1963“Glacial valley stress release”: Ferguson, 1967

• Deformational styles“Sackung”: Zishinsky, 1969;

“Deep creep”: Ter-Stepanian , 1966; “Lateral spreading”: Nemcock and Rybar, 1968;

“Large block sliding”: Zaruba and Mecl, 1969, “Gravitational spreading of ridges”, Varnes et al., 1989

What is a deep-seated gravitational slope deformation?

After Agliardi et al. (2001)

Two main representations

Sackung Lateral Spreading

open fractures

scarps

toe bulging of brittle formations on ductile units

homogeneous rocksBisci et al. (1996)

Varnes (1978)

• Single phenomenon << involved slope• High variable ratio run-out/volume• Deformations “need” a failure/sliding surface

“Deep-seated Gravitational Slope Deformation”

• Phenomenon dimension = involved slope• Low ratio run-out/volume• A sliding surface is not an essential feature (the deformational mechanism is complex)

“Landslide”

Landslide vs DsGSD

Traditional approaches to the study of DsGSD

The geomorphological method:Double ridgesTrenchesElongated depressionsSliding stepsIsolated rock wallsUp hill facing scarpsSlope bulgingsTalus sheets

The structural method:Shear zonesFault scarpsCollapse zonesHorst and GrabenGravitational Thrusts

“Regional Geological Approach” (RGA), Giardino et al. 2009

RGA analyses:• large scale, long-term features• geomorphological, lithological and structural features as general factors of instabilities in the mountain reliefRGA allows interpretation of:• evolutionary stages of the mountain relief• regional variables, offering a “static” conditioning to the system (e.g. lithology as an “internal” cause of DsGSD controlling shear strenght)

© Google 2009

Mathews and Monger, 2005

“Local Morphodinamic Approach” (LMA), Giardino et al. 2009

LMA analyses the characteristic landforms and processes of natural instability, relevant to understand mechanism of one specific DsGSDLMA allows:• the control on dynamic factors of natural instabilities (e.g. the increase of slope gradient as an “external” cause of DsGSD, increasing shear stress )• Process modelling and hazards assessment

http://gsc.nrcan.gc.ca/landslides/photo_library_e.php

© Google 2009

- Formation of DsGSD may be influenced by many factors• Shape/height of slope, lithology, structure, tectonics, groundwater conditions,

glacial history- Necessary to integrate different techniques for a detailed characterization• Aerial Photos• Field mapping• GIS• Numerical modeling

Methods of study

Objectives of my Thesis

1. Establish a conceptual framework for a database of deep-seated gravitational slope deformations in British Columbia and apply it to my case study in the North of the Monashee Complex, in the Seymour Valley (SE British Columbia) (Clague, Giardino, Stead).

2. Develop and integrate the database with the main case studies already described in Europe (in Italy especially) (Giardino, Ghirotti).

3. Perform a field investigation to evaluate the history of slope deformation close to Blais Creek with respect to the tectonic and glacial history of the Seymour Valley (Clague, Giardino, Gibson).

4. Record geotechnical properties of the deforming rock mass for use in numerical models (Stead, Ghirotti).

5. Investigate the failure mechanism at Blais Creek through finite and/or discrete element modeling (Stead, Ghirotti).

Site Description

© Google 2009

The Blais Creek Area• Site suggested by Derek Kinakin•No previous works on DSGsD in this area

• Area within the Monashee Decollment (MD and CRF)

J. Murray Journeay, 1986

• Area between the Okanagan- Eagle River Fault Zone and the Columbia River Fault Zone, both in extension

• Area inside the Northern Frenchman Cap Dome, Omineca Belt, Canadian Cordillera, SE British Columbia

• Area between the Aphebian Basement Terrane (gneiss, paragneiss, amphibolite) and the Mantling Metasedimentary Cover (quartzite, marble)

• Area on the Kymberville Anticline

J. Murray Journeay, 1986

The Geology of Blais Creek

5 km

Main lithostructural characteristics of instability in the Blais Creek Area

• Structural weakness (low angle “Decollment”)• Contact between the Aphebian Basement Terrane and the Mantling Metasedimentary Cover (contrast of competence)• Regional schistosity parallel to the slope (Basement Terrane over the Metasedimentary Cover)• Brittle structures in the Basement Terrane (related probably to the extensional tectonic)• Possible presence of Paleoregolith between the Metasedimentary Cover and the Basement Terrane (fractured, altered and weak material)• Similarity of regional variables conditioning the slope instability of the Downie Slide: lithology and structural setting

“Heritage” of the Evolution of the continental crust in the Monashee Complex

R. L. Brown and J. M. Journeay, 1987

Glacial history in the Seymour Valley

• Slope debuttressing after deglaciation cited as important cause of DsGSD and landsliding

• Ongoing glacier loss in the upper slopes after end of Little Ice Age caused active slope instabilities.

• Last major glaciation ended 11,500 years ago (ice free from main valleys)

© Google 2009

Linear features in the Blais Creek Area

“Passive” origin:Old tectonic linear features

“Active” Origin:Release of energyafter deglaciationor neotectonic orboth

Cross Sections

K

LE E’

LegendDa = marbleDb = quartize

J. Murray Journeay, 1986

Geological SurveyOf Canada, 1964

Methods summary

Field methods:Mapping of surface featuresGeotechnical investigationTrench ?

Laboratory techniquesYield strength of samples collected in the field

Remote sensing and software-aided data analysisPhotogrammetryGIS databaseGeotechnical analysis for numerical modeling

Field methods 1: Surface features

Map geomorphological features:Double ridgesTrenchesElongated depressionsSliding stepsIsolated rock wallsAntislope scarpsSlope bulging Talus sheets

Flow of water into and out of slopeGlacial features and interaction with DsGSD featuresData entered into handheld GPS unit

SRG2 toolbar for ArcPad (modified for this project)

SRG2 toolbar

Detailed geotechnical characterization of the rock mass:

Intact rock strength (Schmidt hammer)Rock mass quality (GSI)Weathering grade andDiscontinuities (ISRM)

Spot measurements, scanlines in select locationsStereo-couple photographs for later photogrammetry

Field methods 2: Geotechnical

www.abbeyspares.co.uk

Field methods 3: trenching ?

•Trench excavated perpendicularly to feature but the antislope scarps are rocky, not the best material for trenching.• Examine stratigraphy of sediment infills if possible

Laboratory methods

• Point load testing of intact rock samples• Strength parameters derived using RocLab software

http://www.enkaymachine.com

• Surface feature mapping on aerial photographs

GISHelp with field planning

• PhotogrammetryJoint mapping at 2-3 outcrops Software: ENVI and 3DM CalibCam and 3DM Analyst (ADAM Technology)

Remote sensing

Year Code No. Type scale

2007 15BCC07018 (9, 10, 11) (33, 34, 35, 36, 37) Color 1:20000

1992 30BCC92065 (6,7,8,9) (61, 62, 63, 64) Color 1:15000

1982 15BC82021 (120, 121) B/W 1:60000

1973 30BC7535 (213, 214, 215) (232, 233, 234) B/W 1:15000

1952 BC1603 (55, 56, 57) (oblique) B/W 1:20000

1952 A13495 (…, 27, …, 63, ) B/W 1:60000

In concert with Gabriel HensoldFormat based on Giardino et al. (2004)

First phase: Inventory of data from past published studies in B.C.

Naming and localization of sitesGeospatial and geotechnical dataInterpretations

Second phase: add the main data from the European (especially Italian) past published studiesThird phase: application of database format to detailed new studies

Blais Creek (me)

DsGSD database

Handcar Peak (Gabriel Hensold)

Outline of data entry format

1. General inventory metadata (ID, data source, date, reporter)2. Geographical position of feature3. Geomorphology of DsGSD

a) DsGSD geometryb) Slope morphologyc) Surface deformation featuresd) Other landforms

4. Hydrology5. Structural geomorphology of Valley slopes

a) Slope and bedding/schistosity relationshipb) Orientations of structural discontinuities (foliation, joints, faults)

6. Geologya) Structural unitsb) Lithological units

7. Geotechnical properties1. Intact rock2. Rock mass3. Discontinuities

Numerical modelling?

• Evaluate failure mechanism at Blais Creek• Possible kinematic analysis using DIPS• Possible RocPlane prelim analysis• Possible Phase2 analysis • Explicit model (FLAC or UDEC)

Continuum or discontinuum? Depends on stress conditions and the rock mass.

Agliardi et al. (2001)

Course:Photogrammetry short course with Matthieu Sturzenegger

Office work:Complete inventory of previous DsGSD studies in B.C. Obtain GIS shape files and Digital Elevation Models from TurinMap surface features at Blais Creek through GIS and Google Earth using digitized aerial photosPlan logistics for field work in Blais Creek and Handcar Peak

Field work:Field research at Blais Creek (3-4 weeks)Field research in Handcar Peak (3-4 weeks)

Timeline: Summer 2009

Timeline: Fall/Winter 2009

• Office work:– Compilation, organization and analysis of spatial and geotechnical data

gathered in the field in a GIS database– Point load strength testing on rock samples from Blais Creek– Creation of initial numerical models

• Departure for Italy (around 20th of September 2009)

• Course:– Final course – Matlab Class at the University of Bologna

• Office work:– Creation of initial numerical models– Begin writing Thesis

Timeline: Spring 2010

Spring Semester 2010Office work:

Finish numerical modelling analysis of Blais CreekFinish writing thesis Thesis Defence (hopefully....)

References

Agliardi F, Crosta G, Zanchi A. 2001. Structural constraints on deep-seated slope deformation kinematics. Engineering Geology 59(1-2):83-102.

Bovis MJ. 1982. Uphill-facing (antislope) scarps in the Coast Mountains, Southwest British Columbia. Geological Society of America Bulletin 93(8):804-812.

Bovis MJ, Evans SG. 1996. Extensive deformations of rock slopes in the southern Coast Mountains, southwest British Columbia, Canada. Engineering Geology 44(1-4):163-182.

Giardino M, Giordan D, Ambrogio S. 2004. G.I.S. technologies for data collection, management and visualization of large slope instabilities: Two applications in the Western Italian Alps. Natural Hazards and Earth System Science 4(2):197-211.

Holm K, Bovis M, Jakob M. 2004. The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia. Geomorphology 57(3-4):201-216.

Jahn A. 1964 Slopes morphological features resulting from gravitation. Annals of Geomorphology 1964:59.

Kinakin D. 2004. Occurrence and Genesis of Alpine Linears Due to Gravitational Deformation in South Western, British Columbia. MSc thesis, Simon Fraser University, Burnaby, BC.

Monger JWH, Journeay JM. 1994. Geology of the Southern Coast and Intermontane Belt. Geological Survey of Canada, Open File 2490, map, scale 1:500,000

Nichol SL, Hungr O, Evans SG. 2002. Large-scale brittle and ductile toppling of rock slopes. Canadian Geotechnical Journal 39:773-788.

Savage WZ, Varnes, DJ. 1987. Mechanics of gravitational spreading of steep-sided ridges. Bulletin of the International Association of Engineering Geology 35(1):31-36.

Stepanek M. 1992. Gravitational deformations of mountain ridges in the Rocky Mountain foothills. Proceedings of the International Symposium on Landslides 6:231-236.

Thank you!

John ClagueDoug Stead Marco GiardinoDan Gibson

And to everyone in the Earth Sciences Department of SFU….