Erosion of the Southern Alps of New Zealand during the last deglaciation

Abstract

During the Quaternary, periodic glaciations transformed mountain landscapes. However, how mountain erosion changes between glacier-and river-dominated conditions has been elusive. Here, using samples from an offshore sedimentary core, we Page 2 of 17 estimate the spatial distribution of erosion in the southern part of the Southern Alps of New Zealand during a full transition from the Last Glacial Maximum (LGM), ~20 ka, to the last millennium. Raman spectroscopy analyses of carbonaceous material reveal a marked change in the sediment provenance, which we interpret to reflect the evolving erosion pattern of the mountain range. Over the Holocene since at least ~9 ka, erosion was focused on the chlorite zone schist within the upper reaches of the valleys (>15-20 km distance from the mountain front), possibly dominated by large-magnitude landslides. During the last glaciation, the proportion of sediments from the biotite schist and highergrade metamorphic rocks in the lower lying areas closer to the mountain front (<15-20 km) was relatively higher, probably the products of glacier carving. Our results suggest that glacier retreat during the last deglaciation caused an upstream localization of the high erosion rates, which is consistent with the snowline records in the Southern Alps and the regional and global climate histories.

Controls on the formation of potential landslide dams and dammed lakes in the Austrian Alps

“…The formerly glaciated areas of the Austrian Alps present highest mean elevations, relief, slopes and uplift rates, and almost all modeled landslides. Further, adjustment of glacial landscapes to deglaciation has been suggested to lead to an increase in hillslope processes (Church and Ryder, 1972;Crest et al, 2017;Jiao et al, 2018). This fits our distribution of landslides and release volumes.…”

Glacial Catchment Erosion From Detrital Zircon (U‐Th)/He Thermochronology: Patagonian Andes

“…In summary, this study and previous studies highlight the potential of tracer applications to investigate glacial erosion over different spatial and temporal scales. Results suggest the importance of the position of the glacial and interglacial ELA to focus erosion (this study; Ehlers et al, 2015;Jiao et al, 2018), and particularly of the glacial ELA with significantly enhanced erosion at and below this zone (this study; Jiao et al, 2018). Furthermore, erosion patterns may change rapidly, also on syn-or post-glacial timescales .…”

“…This change in the focus of erosion corresponds with elevations at and below the LGM and modern ELAs (∼500-700 m and ∼1,000 m higher, respectively). At least for the glacial erosion signal, we can compare this focused erosion at the ELA during glacial episodes to our study, although our results reflect one glacial catchment and Jiao et al's (2018) samples reflect an integrated signal from a large catchment area and over different timespans.…”

“…Finally, Jiao et al (2018) used Raman spectroscopy of carbonaceous material from a sediment core offshore of the Southern Alps, New Zealand (44°S). The catchment area encompassed several glacial catchments (catchment area of ∼130 × 30 km) where the elevation distribution of erosion was traceable due to a spatial gradient in the metamorphic grade of exposed schist.…”

“…Nevertheless, these mechanisms are poorly understood and the uncertain distribution of subglacial erosion and temporal variations in glacial mechanics complicate investigations (e.g., Fernandez et al, 2011;Herman et al, 2011;Humphrey & Raymond, 1994;Ugelvig & Egholm, 2018). Observational data capable of testing model predictions of glacial erosion and sediment production are limited, and so far derive largely from thermochronologic methods (Clinger et al, 2020;Ehlers et al, 2015;Stock et al, 2006;Tranel et al, 2011) and Raman spectroscopy of carbonaceous material to track the provenance of eroded material below glaciers Jiao et al, 2018).…”