Advertisement

Gravitational spreading of steep-sided ridges (“sackung”) in Western United States

  • Radbruch-Hall D. H. 
  • Varnes D. J. 
  • Savage W. Z. 
Section 13 Engineering Geology

Summary

Large-scale gravitational spreading and movement along fractures of steep-sided ridges in the mountainous areas of the western United States are characterized by linear fissures, trenches, and uphill-facing scarps on tops and sides of ridges. Spreading appears to take place by movement along disconnected planes and/or by slow plastic deformation of a rock mass. In some places, valleyward squeezing out of weak shales overlain by rigid rocks causes extensional fracturing and outward movement of the rigid layers, as illustrated by extension of two laccoliths overlying Mancos Shale, one at Dolores Peak and another at Crested Butte in western Colorado. Gravitational forces acting on a ridge of more homogeneous material causes tensional spreading of the ridge parallel to its long axis, for example in fractured granitic rock north of Mt. Massive in central Colorado, where a survey course has been established to monitor the movement. Recognition and understanding of these large-scale gravitational features and the mechanism that causes them are pertinent to site selection and design of engineering structures in high mountains. If fractures extend to considerable depth and if movement is continuing, engineering structures in valleys or tunnels through the spreading ridges could be damaged.

Keywords

Shale Trench Aerial Photograph East Side Stereo Pair 

Etalement, Du A La Force De Gravitation, D’aretes Montagneuses A Pente Accentuée (Sackung) Dans L’ouest Des Etats-Unis D’amérique

Résumé

L’étalement à grande échelle causé par la force de gravitation et le mouvement le long de fractures affectant les arêtes à pente accentuée dans les régions montagneuses de l’ouest des Etats-Unis d’Amérique sont caractérisés par des fissures linéaires, des fossés et des escarpements façant l’amont, localisés sur les sommêts et les versants des crêtes. L’étalement semble prendre place par mouvement le long de plans disjoints, et/ou par déformation plastique lente d’une masse rocheuse. Dans quelques localités, l’extrusion vers l’aval d’argiles schisteuses meubles surmontées par des roches rigides cause des fractures d’extension et un mouvement des couches rigides vers l’extérieur, comme le montre l’extension de deux laccolites recouvrant l’argile schisteuse de Mancos (l’un à Dolores Peak et l’autre à Crested Butte, dans l’ouest du Colorado). Les forces de gravitation agissant sur une crête formée dans un matériau plus homogène causent l’étalement de la crête par tension le long de son axe longitudinal; par exemple dans la roche granitique fracturée au nord du Mt. Massive dans le Colorado central, òu des mesures d’arpentage sont faites régulièrement pour contrôler le mouvement. La reconnaissance et la compréhension de ces phénomènes à grande échelle dus à la force de gravitation et de leurs mécanismes sont utiles à la sélection des sites de construction et au calcul des ouvrages d’art en haute montagne. Si les fractures s’étendent à des profondeurs considérables et si le mouvement continue a présent, les ouvrages d’art situés dans les vallées ou les tunnels transversaux aux crêtes qui s’étalent peuvent être endommagés.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. BARLA G. (1973): Application of the finite element method in the analysis of rock slopes: Geologia Applicata e Idrogeologia, v. 8, pt. 1, p. 343–352.Google Scholar
  2. BECK A.C. (1968): Gravity faulting as a mechanism of topographic adjustment: New Zealand Jour. Geology and Geophysics, v. 11, no. 1, p. 191–199.CrossRefGoogle Scholar
  3. BRAY J.W. (1967): A study of jointed and fractured rock, Part I, Fracture patterns and their characteristics: Rock Mechanics and Engineering Geology, v. 2–3, p. 118–136.Google Scholar
  4. BUSH A.L. — BROMFIELD C.S. (1966) : Geologic map of the Dolores Peak quadrangle, Dolores and San Miguel Counties, Colorado: U.S. Geol. Survey Geol. Quad. Map GQ-536.Google Scholar
  5. FOLBERTH P.J. (1965) : Beitrag zur rechnerischen Ermittlung der Spannungszustände in Felsbauwerken [Contribution to the analysis of stress conditions in rock structures]: Rock Mechanics and Engineering Geology, Supplementum II, p. 25–33.Google Scholar
  6. HANDIN John (1966): Strength and ductility,in Handbook of physical constants, rev. ed., S.P. Clark, Jr., ed.: Geol. Soc. America Mem. 97, p. 223–289.CrossRefGoogle Scholar
  7. JONES W.R. — PEOPLES J.W. — HOWLAND A.L. (1960): Igneous and tectonic structures of the Stillwater Complex, Montana: U.S. Geol. Survey Bull. 1071-H, p. 281–335.Google Scholar
  8. KOBAYSHI Kunio (1956) : Periglacial morphology in Japan: Builetyn Periglacjalny Nr. 4, p. 15–36 (Lodzkie towarzystwo naukowe societas scientarium lodziensis, Wydzial III, sectio III).Google Scholar
  9. NEMČOK Arnold (1972): Gravitational slope deformation in high mountains: Internat. Geol. Cong., 24th, Montreal, Canada, sec. 13, Proc., p. 132–141.Google Scholar
  10. PECK Ralph B. (1967): Stability of natural slopes: Am. Soc. Civil Engineers Proc., Jour. of the Soil Mechanics and Foundations Div., v. 93, no. SM4, p. 403–417.Google Scholar
  11. ROBINSON C.S. — LEE F.T. and others (1972) : Geological, geophysical, and engineering investigations of the Loveland Basin landslide, Clear Creek County, Colorado, 1963–65: U.S. Geol. Survey Prof. Paper 673-A through G, 43 p.Google Scholar
  12. SOULE J.M. (1976) : Geologic hazards in the Crested Butte-Gunnison area, Gunnison County, Colorado: Colo. Geol. Survey Open-File Rept., plates 2 and 4 of 9 plates.Google Scholar
  13. STINI Josef (1941): Unsere Täler wachsen zu: Geologie und Bauwesen, Jahrg. 13, H. 3, p. 71–79.Google Scholar
  14. STINI Josef (1952): Neuere Ansichten über “Bodenbewegungen” über Beherrschung durch den Ingenieur: Geologie und Bauwesen, Jahrg. 19, H. 1, p. 31–54. (English translations of the above two references are available from the Austrian Society for Geomechanics Translation Service: Müller, Leopold, ed., 1974, Josef Stini, excerpts from his publications on landslides, engineering geology of dams and reservoirs, tunneling, groundwater effects in rock masses and tectonics (Introduction by A. Kieslinger): Publication No. 18, Österreichische Gesellschaft für Geomechanik, Übersetzungsdienst, 5020 Salzburg (Austria) Franz-Josef-Strasse 3/111.)Google Scholar
  15. TWETO Ogden (1974) : Geologic map and sections of the Holy Cross quadrangle, Eagle, Lake, Pitkin, and Summit Counties, Colorado: U.S. Geol. Survey Misc. Invest. Ser. Map I-830.Google Scholar
  16. VARNES David J. (1958) : Landslide types and processes,in Eckel, E.B., ed., Landslides and engineering practice: Highway Research Board Special Report 29, NAS-NRC Publication 544, p. 20–47.Google Scholar
  17. YEEND Warren E. (1969) : Quaternary geology of the Grand and Battlement Mesas area, Colorado: U.S. Geol. Survey Prof. Paper 617, 50 p.Google Scholar
  18. YEEND Warren E. (1973): Slow-sliding slumps, Grand Mesa, Colorado: The Mountain Geologist, v. 10, no. 1, p. 25–28.Google Scholar
  19. ZISCHINSKY Ulf (1966): On the deformation of high slopes: Internat. Soc. Rock Mechanics Cong., 1st, Lisbon, Proc., v. 2, p. 179–185.Google Scholar
  20. ZISCHINSKY Ulf (1969): Uber Sackungen: Rock Mechanics, v. 1, p. 30–52.CrossRefGoogle Scholar

Copyright information

© International Association of Engineering Geology 1976

Authors and Affiliations

  • Radbruch-Hall D. H. 
    • 1
  • Varnes D. J. 
    • 2
  • Savage W. Z. 
    • 2
  1. 1.U.S. Geological SurveyCaliforniaU.S.A.
  2. 2.U.S. Geological Survey, MS 903DenverU.S.A.

Personalised recommendations