Schmidt‐hammer exposure‐age dating (SHD) of snow‐avalanche impact ramparts in southern Norway: approaches, results and implications for landform age, dynamics and development. Issue 13 (23rd May 2015)

• Record Type: Journal Article
• Authors: Matthews, John A.; McEwen, Lindsey J.; Owen, Geraint
• Is Part Of: Earth surface processes and landforms. Volume 40:Issue 13(2015)
• Page Start: 1705
• Page End: 1718
• Publication Date: 2015-05-23
• Subjects: Geomorphology -- Periodicals; 551.4
• DOI: 10.1002/esp.3746
• Languages: English
• ISSNs: 0197-9337

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>Schmidt‐hammer exposure‐age dating (SHD) was applied to the problem of dating the diachronous surfaces of five distal river‐bank boulder ramparts deposited by snow avalanches plunging into the Jostedøla and Sprongdøla rivers in the Jostedalsbreen region of southern Norway. Approaches to local high‐precision linear age calibration, which controlled in different ways for boulder roundness, were developed. The mean age (SHD<italic><sub>mean</sub></italic>) and the maximum age (SHD<italic><sub>max</sub></italic>) of surface boulders were estimated for whole ramparts, crests and distal fringes. Interpretation was further assisted by reference to R‐value distributions. SHD<italic><sub>mean</sub></italic> ages (with 95% confidence intervals) ranged from 520 ± 270 years to 5375 ± 965 years, whereas SHD<italic><sub>max</sub></italic> ages (expected to be exceeded by <5% of surface boulders) ranged from 675 to 9065 years. SHD ages from the Jostedøla ramparts tended to be older than those associated with the Sprongdøla, rampart crests were younger than the respective distal fringes, and use of relatively rounded boulders yielded more consistent SHD ages than angular boulders. The SHD<italic><sub>mean</sub></italic> ages indicate differences in recent levels of snow‐avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and, in smaller numbers, on the distal fringes. SHD<italic><sub>max</sub></italic> ages provide minimum age estimates of rampart age (i.e. the time elapsed since the ramparts began to form) and suggest that at least some of the ramparts have been developing since the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd.</p> </abstract>