Cliff-height and slope-angle relationships in a chronosequence of Quaternary marine terraces, San Clemente Island, California

Authors

Russell Crittenden, University of Wisconsin-Madison
Daniel R. Muhs, U.S. Geological SurveyFollow

Date of this Version

9-1986

Citation

Z. Geomorph. N. F. 30:3, pp. 291-301 (Berlin & Stuttgart: September 1986)

Comments

U.S. government work

Abstract

Zusammenfassung. Eine Abfolge quartarer Strandterrassen auf ~an Clemente Island, Kalifornien, liefert einen Rahmen fur die quantitative Analyse der Anderungen an vom Meer verlassenen Kustenkliffen als Funktion der Zeit. Es wurde eine Abschatzung der Anwendbarkeit von BUCKNAM & ANDERSON (1979) log-lin~arer Beziehung zwischen Wandhohe und Hangwinkel durchgefuhrt, indem Brandungskliffhohe und maximale Hangwinkel verwendet wurden. Die Ergebnisse zeigen eine regelhafte Zunahme des Hangwinkels mit dem Logarithmus der Kliffhohe, und Kliffe einer bestimmten Hohe zeigen m,it der Zeit eine Abnahmedes maximalen Hangwinkels. 1m ganzen waren die Relationen schwacher als fur FluBterrassen und Bruchstufen in unverfestigten Materialen, aber die Methode kann wahrscheinlich verwendet werden, urn fruhe, mittlere und junge quartare Bruchstufen und Kustenkliffe in verfestigtem Material erfolgreich zu unterscheiden.

Summary. A flight of Quaternary marine terraces on San Clemente Island, California, provides a framework for quantitative analysis of abandoned sea cliff modification as a function of time. An assessment was made of the applicability of BUCKNAM & ANDERSON'S (1979) log-linear relationship between scarp height and slope angle using sea cliff height and maximum slope angle. Results indicate a regular increase in slope angle with the logarithm of the cliff height and cliffs of a given height show a decline in maximum slope angle with time. Overall, the relationships are weaker than for stream terraces and fault scarps in unconsolidated materials, but the method can probably be used successfully to distinguish early, middle and late Quaternary fault scarps or sea cliffs in consolidated materials.

Resume. Une serie de terrasses marines quaternaires sur l'ile de San Clemente (Californie) fournit un cadre pour l'analyse quantitative de l'evolution de falaises marines mortes. Une hypothese a ete avancee concernant l'application de la relation log-normale de BUCKNAM & ANDERSON (1979) entre la hauteur de l'escarpement et l'angle de la pente appliquee ici a la hauteur de la falaise marine et l'angle maximum de la pente. Les resultats indiquent un accroissement regulier de la pente avec Ie logarithme de la hauteur de la falaise et les falaises d'une hauteur determinee montrent un abaissement de l'angle de pente maximum en fonction du temps. Partout, les relations sont moins bonnes que pour les terrasses de rivieres et des escarpements de failles dans des materiaux meubles. Toutefois, la methode peut probablerment etre utilisee avec succes pour donner un age quaternaire recent moyen ou ancien aux escarpements de failles ou aux falaises marines dans des materiaux c;onsolides.

Text in English: The rate of alteration of slopes, particularly those derived from fault scarps, has received increasing attention in recent years because of the need for accurate assessment' of potential fault hazards (WALLACE 1977; BUCKNAM & ANDERSON, 1979; NASH 1980a, 1980b, 1984; MACHETTE 1982; COLMAN 1983; COLMAN & WATSON 1983; HANKS et al. 1984; MAYER 1984; STERR 1985). Often there is a need for age determination of a fault scarp, but little or no material available for radiometric dates. Hence, many investigators have utilized morphometric parameters in order to establish relative and in some cases absolute ages. BUCKNAM & ANDERSON (1979) were perhaps the first to quantify changes in fault scarp slope angles through time. They examined the relationship between scarp height and slope angle in Quaternary deposits in the Great Basin of western Utah and quantified earlier observations of WALLACE (1977). Their results indicated that for small scarps less than 10 m high, slope angle increases with the logarithm of scarp height and decreases through time for a scarp of a given height. This relationship has been confirmed for fault scarps in other locations in the southwestern U. S. A. (MACHETTE 1982; MAYER 1984; HANKS et al. 1984) and has been, extended to other landforms such as stream terrace scarps (COLMAN 1983) and lake cliffs (NASH 1980b). Several studies have gone beyond the relative dating method proposed by BUCKNAM & ANDERSON (1979) and models for determination of absolute age have been generated (NASH 1980b, 1984; COLMAN & WATSON 1983; HANKS et al. 1984; HANKS & WALLACE 1985; STERR 1985). MAYER (1984) recently discussed the complicating effects of measurement error, lithology, particle size, and composite scarps.