Chronology of Holocene rock-avalanche deposits based on Schmidt-hammer relative dating and dust stratigraphy in nearby bog deposits, Vora, inner Nordfjord, Norway

Abstract

A number of large rock avalanches from the northern slope of the 1435 m high mountain of Vora in Breim, inner Nordfjord have been mapped. The avalanche tongues dam the 4 km long Sandalsvatnet, they cover an area of 3 km 2 and the volume exceeds 100 million m3. Age estimates have been obtained by radiocarbon datings of rock dust layers in a bog and the Schmidt-hammer method. Altogether 11 large rock avalanches have occurred throughout the Holocene, of which six lobes can be recognized morphologically. Five silt laminae in a 5.5 m deep bog basin distally to the avalanche lobes are interpreted as primary sediments from dust clouds generated by rock avalanches. In addition three silt beds are interpreted as glaciolacustrine sediments related to temporary damming caused by landsliding. Average avalanche frequency during the Holocene was c. 1 per 1000 yr and during the period 7100—3600 BP it was c. 1 per 700 yr. After 3600 BP no rock avalanches have been recognized.

First attempt to combine terrestrial cosmogenic nuclide (10Be) and Schmidt hammer relative-age dating: Strauchon Glacier, Southern Alps, New Zealand

“…Different strategies have been developed in order to solve this problem, one is to calculate a calibration curve based on fixed points (ages) derived from radiocarbon ( 14 C) dating [19,[41][42][43]. Crucially, this relies on finding datable organic material with an unambiguous relationship to the chosen site of surface exposure dated by the Schmidt hammer.…”

“…[34,41]; cf. discussion [43]. Giving the late-Holocene age of the moraine system according to the result of the TCND, a linear relationship seems to be a reasonable assumption.…”

“…In a geochronological context, the Schmidt hammer is widely used as a relative-age dating technique on glacially eroded bedrock surfaces, boulders embedded in glacial deposits, rock glaciers and talus, e.g. [19,29,[35][36][37][38][39][40][41][42][43][44][45][46]. The measurement of surface hardness of rock surfaces reveals information on their exposure to subaerial weathering processes and, therefore, on the relative-age of related moraine formations.…”

“…Although radiocarbon dating has previously been used for calibration and 'absolute' dating of Schmidt hammer measurements e.g. [19,[41][42][43], the genetic and chronological relationship between the organic material dated and exposure ages of the boulders on the moraines is not always simple and undisputable.…”

Time constraints for the evolution of a large slope collapse in karstified mountainous terrain of the southwestern Crimean Mountains, Ukraine

“…Hence it is useful to find and extend a set of possible dating strategies and morphostratigraphical features which could be used in the dating of slope deformations. Some new landslide-dating strategies are presented by Becker and Davenport (2003), Aa et al (2007) and Takagi et al (2007).…”