Ralph Böhlert

Bio: Ralph Böhlert is an academic researcher from University of Zurich. The author has contributed to research in topics: Rock glacier & Surface exposure dating. The author has an hindex of 7, co-authored 9 publications receiving 194 citations.

Landscape evolution in Val Mulix, eastern Swiss Alps – soil chemical and mineralogical analyses as age proxies

Abstract: Towards the end of the last glacial cycle, repeated re-advances of valley glaciers in the European Alps combined with periglacial processes led to the formation of a variety of climate-related landforms. Independent age measurements of moraines and rock glacier lobes using both in-situ produced and meteoric 10Be allows for the use of soil formation as an age proxy. In this complementary study we present chemical and mineralogical data from five Podzols from Val Mulix in Eastern Switzerland. Two of them developed on granitic Lateglacial moraines (14.9 ka and 10.7 ka, respectively) and three were sampled on lobes of a morphostratigraphically connected relict rock glacier, covering an age range of approx. 10.7 ka to 8.6 ka. Besides the evaluation of the suitability of selected pedosignatures for a relative age separation, we hypothesised that these pedosignatures should give further information about the evolution of the specific sites. Although the soils had a high skeleton content and the oldest soil started its development in a slightly colder climatic phase, typical weathering trends could still be detected. Whereas weathering indices such as the (K + Ca)/Ti ratio or the B-index reflect time trends reasonably well, the mineralogical composition of the fine earth and clay fraction yielded a slightly more inconsistent picture; to a lesser extent, some inconsistencies were also exhibited when using the weathering mass balance approach. This is especially true for the relict rock glacier and it supports the suggested complex development history of these soils as well as the presence of pre-weathered material. Techniques that include several surface soil horizons and the soil skeleton such as the (K + Ca)/Ti ratio, the B-index and the mass balance approach gave more robust results (in terms of the expected chronology) than the ones that only referred to single horizons (clay mineralogy). Errors or variations due to potential reallocation processes within the soil horizons but without a prominent change of the overall soil characteristics are minimised using such an approach. Weathering indexes and the clay mineral assemblage provided a differentiation of soils even within a relatively narrow time range and gave insight into processes that have occurred at the specific sites. The combined relative-numerical dating approach used here not only enables an extended interpretation and mutual control, but ultimately leads to a better understanding of landscape reconstruction and evolution.

Glacier variations in the European Alps at the end of the last glaciation

Abstract: The Last Glacial Maximum in the Alps lasted from approximately 30 to 19 ka. Glaciers reached out onto the forelands on both sides of the main Alpine chains, forming piedmont lobes in the north and filling the Italian amphitheatres to the south. Pullback of glaciers from their maximum extent was underway by 24 ka. Glaciers oscillated at stillstand and minor re-advance positions for several thousand years forming Last Glacial Maximum (LGM) stadial moraines. North and south of the Alps, the various stadials cannot yet be unequivocally matched. Glaciers had receded back within the mountain front by 19-18 ka. During the early Lateglacial phase of ice decay remnants of the once huge valley glaciers that fed the piedmont lobes downwasted and were likely calving into the extensive lakes that formed in the lower valley reaches. The first Alpine-wide glacier re-advance took place during the Gschnitz stadial, 17-16 ka, which was likely a response to Europe-wide cooling during Heinrich event 1. By the Bolling/Allerod interstadial much of the Alps were ice-free. Glaciers advanced repeatedly to an extent several kilometers from the cirque headwalls, during the Egesen stadial in response to the Younger Dryas cold period. Egesen stadial moraines, at some sites several sets of moraines, were constructed in valleys all across the Alps. 10 Be exposure dates for Egesen stadial moraines are in the range 13.5 to 12 ka. Moraines located at an intermediate position between the Little Ice Age moraines and the Egesen moraines formed at the margins of glaciers that advanced during the closing phase of the Egesen stadial or during the earliest Holocene at 10.5 ka.

A cosmic trip: 25 years of cosmogenic nuclides in geology

Abstract: Terrestrial cosmogenic nuclides, produced by secondary cosmic-ray interactions in the atmosphere and in situ within minerals in the shallow lithosphere, are widely used to date surface exposure of rocks and sediments, to estimate erosion and weathering rates, and to date sediment deposition or burial. Their use has transformed geomorphology and Quaternary geology, for the first time allowing landforms to be dated and denudation rates to be measured over soil-forming time scales. The application of cosmogenic nuclides to geology began soon after the invention of accelerator mass spectrometry (AMS) in 1977 and increased dramatically with the measurement of in situ–produced nuclides in mineral grains near Earth’s surface in the 1980s. The past 25 yr have witnessed the development of cosmogenic nuclides from their initial detection to their prevalence today as a standard geochronological and geochemical tool. This review covers the major developments of the past 25 yr by comparing the state of the field in 1988 with that of today, and by identifying key advances in that period that moved the field forward. We emphasize the most commonly used in situ–produced nuclides measured by AMS for geological applications, but we also discuss other nuclides where their applications overlap. Our review covers AMS instrumentation, cosmogenic nuclide production rates, the methods of surface exposure dating, measurement of erosion and weathering, and burial dating, and meteoric 10 Be. —In memoriam: Devendra Lal (1929–2012), whose vision inspired the field.