Alpine relief limited by glacial occupation time

Geology ◽  
2021 ◽  
Author(s):  
Bernhard Salcher ◽  
Günther Prasicek ◽  
Sebastian Baumann ◽  
Florian Kober
Keyword(s):  
Feedback Loop ◽  
Occupation Time ◽  
Central Alps ◽  
Key Factors ◽  
Equilibrium Line Altitude ◽  
Glacial Erosion ◽  
Cumulative Impact ◽  
Uplift Rates ◽  
Steep Slopes ◽  
Topographic Relief

Glaciers exert a major control on the shape of mountain topography. They tend to reduce relief above and scour troughs below the equilibrium line altitude (ELA). While many studies report this dichotomy, relief-limiting effects are controversial due to difficulties in quantifying key factors such as the initial topography, the timing of glacial occupancy, or rock uplift counteracting glacial erosion. Consequently, effectivity and degree of glacial erosion remain ambiguous. In geologically and climatically well-investigated parts of the European Central Alps, our calculation of glacial occupation time (GOT) from Quaternary ELA variations allows the quantification of gradual topographic modifications generated by the cumulative impact of cirque erosion over the Quaternary. We show that under low uplift, relief is effectively limited by glacial and periglacial headwall retreat, leading to a decline in topographic relief as GOT increases. Conversely, higher uplift rates seem to induce more persistent valley glaciation, triggering a positive feedback loop in which steep slopes are protected against erosion and relief increases.

scholarly journals Analytical long-profile models of coupled glacier-fluvial systems

2020 ◽  
Author(s):  
Eric Deal ◽  
Günther Prasicek
Keyword(s):  
Steady State ◽  
Steady State Solution ◽  
Climatic Conditions ◽  
Tectonic Geomorphology ◽  
Uplift Rate ◽  
Equilibrium Line Altitude ◽  
Glacial Erosion ◽  
Deep Time ◽  
Fluvial Systems ◽  
Uplift Rates

<p>Glaciers are an effective agent of erosion and landscape evolution, capable of driving high rates of erosion and sediment production. Glacial erosion is therefore an important process mediating the effect of climate on erosion rates and tectonics. Further, as a source of sediment, glacial erosion also has implications for the carbon and silicate cycles, with the potential for longterm feedbacks.  Understanding the interaction of climate, tectonics, glacial erosion and topography will lead to more insight into how glaciers can impact these processes. Simple, analytical long-profile models of fluvial incision are fundamental in tectonic geomorphology and critical for addressing fluvial analogues of problems such as those posed above. The advantage of these simple long-profile models is that they can be applied when information about forcing and boundary conditions is minimal (e.g. in deep time), and they can aid in the development of intuition about how such systems respond in general to different forcing. While models of glacial erosion have existed for quite some time, they tend to be complicated and computationally expensive. Currently, analytical long-profile models do not exist for glacial systems. At the same time, the patterns of glacial erosion and sediment transport, and how these processes respond to climate is fundamentally different than fluvial systems, and cannot be addressed properly with purely fluvial models.</p><p>Building on previous work, we introduce several simplifications to make the equations for coupled glacier-fluvial long-profile models easier to use and show that these simplifications have minimal effect on the steady state solution. We then use these new equations to develop an analytical solution for glacier-fluvial long-profiles at erosional steady state. The solution provides glacier geometry, including length and slope, ice thickness, and overall orogen relief for a given uplift rate, rock erodibility, profile length and climatic conditions. To explore the effect of glaciation on the balance between climate, erosion and orogen geometry, we integrate this solution into a critical wedge orogen theory. We find that the total orogen relief should be closely tied to the equilibrium line altitude (ELA), in line with the glacial buzzsaw theory. In addition, our theory predicts that the geometry and average uplift rate of glaciated critical wedge orogens respond more sensitively to changes in climate than those dominated by fluvial erosion. We suggest that the lowered ELA during glacial maxima over the last few million years could have triggered narrowing of critical orogens, with an associated increase in uplift rates within the active orogen core. </p>

scholarly journals Glacial limitation of tropical mountain height

2019 ◽  
Vol 7 (1) ◽  
pp. 147-169 ◽  
Author(s):  
Maxwell T. Cunningham ◽  
Colin P. Stark ◽  
Michael R. Kaplan ◽  
Joerg M. Schaefer
Keyword(s):  
Steady State ◽  
Mountain Range ◽  
Equilibrium Line Altitude ◽  
Glacial Erosion ◽  
Tropical Mountains ◽  
Base Level ◽  
Snow Line ◽  
Bedrock River Incision ◽  
High Tropical Mountains ◽  
The Tropics

Abstract. Absent glacial erosion, mountain range height is limited by the rate of bedrock river incision and is thought to asymptote to a steady-state elevation as erosion and rock uplift rates converge. For glaciated mountains, there is evidence that range height is limited by glacial erosion rates, which vary cyclically with glaciations. The strongest evidence for glacial limitation is at midlatitudes, where range-scale hypsometric maxima (modal elevations) lie within the bounds of Late Pleistocene snow line variation. In the tropics, where mountain glaciation is sparse, range elevation is generally considered to be fluvially limited and glacial limitation is discounted. Here we present topographic evidence to the contrary. By applying both old and new methods of hypsometric analysis to high mountains in the tropics, we show that (a) the majority are subject to glacial erosion linked to a perched base level set by the snow line or equilibrium line altitude (ELA) and (b) many truncate through glacial erosion towards the cold-phase ELA. Evaluation of the hypsometric analyses at two field sites where glacial limitation is seemingly marginal reveals how glaciofluvial processes act in tandem to accelerate erosion near the cold-phase ELA during warm phases and to reduce their preservation potential. We conclude that glacial erosion truncates high tropical mountains on a cyclic basis: zones of glacial erosion expand during cold periods and contract during warm periods as fluvially driven escarpments encroach and destroy evidence of glacial action. The inherent disequilibrium of this glaciofluvial limitation complicates the concept of time-averaged erosional steady state, making it meaningful only on long timescales far exceeding the interval between major glaciations.

scholarly journals The morphology of supraglacial lake ogives

2013 ◽  
Vol 59 (215) ◽  
pp. 533-544 ◽  
Author(s):  
K.N. Darnell ◽  
J.M. Amundson ◽  
L.M. Cathles ◽  
D.R. MacAyeal
Keyword(s):  
Remote Sensing Data ◽  
Spatial Separation ◽  
Equilibrium Line Altitude ◽  
Lake Ice ◽  
Supraglacial Lakes ◽  
Ice Surface ◽  
Physically Based ◽  
Ice Flows ◽  
Fixed Reference ◽  
Topographic Relief

AbstractSupraglacial lakes on grounded regions of the Greenland and Antarctic ice sheets sometimes produce ‘lake ogives’ or banded structures that sweep downstream from the lakes. Using a variety of remote-sensing data, we demonstrate that lake ogives originate from supraglacial lakes that form each year in the same bedrock-fixed location near the equilibrium-line altitude. As the ice flows underneath one of these lakes, an ‘image’ of the lake is imprinted on the ice surface both by summer-season ablation and by superimposed ice (lake ice) formation. Ogives associated with a lake are sequenced in time, with the downstream ogives being the oldest, and with spatial separation equal to the local annual ice displacement. In addition, lake ogives can have decimeter- to meter-scale topographic relief, much like wave ogives that form below icefalls on alpine glaciers. Our observations highlight the fact that lake ogives, and other related surface features, are a consequence of hydrological processes in a bedrock-fixed reference frame. These features should arise naturally from physically based thermodynamic models of supraglacial water transport, and thus they may serve as fiducial features that help to test the performance of such models.

scholarly journals Paleoclimatic interpretation of the early Late-glacial glacier in the Gschnitz valley, central Alps, Austria

1999 ◽  
Vol 28 ◽  
pp. 135-140 ◽  
Author(s):  
Hanns Kerschner ◽  
Susan Ivy-Ochs ◽  
Christian Schlüchter
Keyword(s):  
Cross Sections ◽  
Climate Models ◽  
Younger Dryas ◽  
Late Glacial ◽  
Point Of View ◽  
Central Alps ◽  
Equilibrium Line Altitude ◽  
Glacial Chronology ◽  
The Alps ◽  
Early Late

AbstractThe former glacier at the type locality of the “Gschnitz Stadial” of the Alpine Late-glacial chronology is interpreted from a paleoglaciological and paleoclimatological point of view. The equilibrium-line altitude, ice flux through selected cross sections and mass-balance gradients are calculated from reconstructed glacier topography. They are used to determine total net ablation and accumulation and precipitation under the assumption of steady-state. The former temperature at the ELA and temperature change is estimated using various glacier—climate models. Precipitation was less than one-third of today’s values, and summer temperature was roughly 10°C lower than today. The climate during the Gschnitz Stadial appears to have been cold and continental, and was more similar to full glacial conditions than to the Younger Dryas climate in the Alps. This is further evidence for an older age of the Gschnitz Stadial.

Present-day sediment dynamics and provenance of the Gornergletscher

2021 ◽  
Author(s):  
Fien De Doncker ◽  
Frédéric Herman ◽  
Günther Prasicek ◽  
Thierry Adatte ◽  
François Mettra ◽  
...  
Keyword(s):  
Erosion Rate ◽  
Protective Layer ◽  
Suspended Sediments ◽  
Equilibrium Line Altitude ◽  
Glacial Erosion ◽  
Erosion Rates ◽  
Erosion Processes ◽  
The North ◽  
North Eastern ◽  
Western Side

<p>Glacial erosion processes shape the Earth’s surface. Nevertheless, the processes that drive glacial erosion and the subsequent export of sediments are poorly understood and quantified. These processes include ice sliding, which controls erosion by abrasion and quarrying, and meltwater availability, which is essential to flush out sediment stocks that form a protective layer of sediments impeding bedrock erosion. Mapping glacial erosion rates can help understand the role of these different processes through the spatial relationships between the subprocesses and erosion rates. Here we report timeseries of glacial erosion rate maps inferred from the inversion of suspended sediment loads and their provenance. Geographically, we focus on the Gornergletscher complex (VS, Switzerland) where we collected data for the summer of 2017. The erosion rate timeseries are then compared to records of temperature, precipitation and estimates of discharge and turbidity of the meltwater river. Erosional activity seems to increase with rising temperatures and meltwater discharge, leading to an increased proportion of suspended sediments coming from the north-eastern (and occasionally western) side of the glacier. Interestingly, the peak in sediments from the north-eastern side is always preceded by a peak in sediments from the western side of the glacier. Sediments of these two zones are predominant in the suspended load signal when the maximal temperature at the Equilibrium Line Altitude (ELA) is above 10°C and on the rising limb of the hydrograph. Furthermore, the obtained erosion rate maps suggest that sliding velocities are not the only explanatory factor of the erosion rate patterns. We therefore postulate from these preliminary results that the present-day sediment output of the Gornergletscher complex is largely influenced by short term variations in temperature and meltwater availability.</p>

Numerically simulated ice dynamics and erosion patterns under specific climate scenarios

2020 ◽  
Author(s):  
Fabio Magrani ◽  
Pierre Valla ◽  
David Egholm
Keyword(s):  
Mass Balance ◽  
Ice Thickness ◽  
Climate Scenarios ◽  
Equilibrium Line Altitude ◽  
Geophysical Research ◽  
Glacial Erosion ◽  
Ice Dynamics ◽  
Basal Sliding ◽  
Precipitation And Temperature

<p>Numerical modeling already demonstrated to be a powerful tool for investigating the role of surface processes, including glaciation, in landscape evolution. Ice model developments from 1-D simulations (Oerlemans, 1984; MacGregor et al., 2000) to more recent 2-/3D models (e.g. Egholm et al., 2011) allow investigating glacier dynamics and landscape erosion over various timescales by also incorporating the effects of rugged topography and feedbacks between erosion by glacial sliding and the extent of glaciation.</p><p>Precipitation and temperature are primary controls on glacier mass balance, driving basal sliding and erosion in response to changes in both ice thickness and extent. However, still little is known on how erosion patterns behave under temporally- and spatially-varying combinations of these two climatic parameters. Since ice basal sliding and fluctuations of water-pressure peak around the equilibrium-line altitude (ELA) (MacGregor et al., 2000; Herman et al., 2011), erosion would be expected to follow similar patterns due to their relationship with abrasion and quarrying. However, modeled glaciers with similar geographical extents may present significant differences in either ice thickness and/or ELA, depending on the simulated climate scenarios (i.e. combinations of precipitation/temperature). This will in turn affect ice dynamics and thus erosion patterns, especially differences between the accumulation and ablation areas.</p><p>In this study we aim to numerically explore how both ice dynamics and erosion patterns are influenced by specific climatic scenarios (i.e. precipitation and temperature conditions). Towards this, we used the Integrate Second Order Shallow Ice Approximation - iSOSIA (Egholm et al., 2011) model, which uses a positive degree-day (PDD) model for mass balance and a depth-integrated computation for ice flux with irregular Voronoi cell grids, allowing local mesh adjustments in selected topographic areas. In addition, this model is capable to couple ice, water and sediments which permits to explore erosion feedbacks onto ice dynamics.</p><p>Using a synthetic Alpine landscape, we performed a set of simulations with mass balance scenarios preserving similar ELAs and ice extents between runs. From these simulations, we generated glacial erosion patterns (e.g. steady-state erosion, total erosion integrated over a glacial cycle), testing different erosion laws (abrasion, quarrying) as well as the role of subglacial water and sediment entrainment. From the different scenarios, we also investigated how ice dynamics (i.e. ice flux and thickness) and erosion rates vary spatially and differ between the accumulation/ablation areas. Our ultimate goal is to understand how glacial erosion patterns, combined with classic paleo-glacial reconstructions and paleo-ELA estimates, can be used as proxies for paleoclimate reconstruction.</p><p> </p><p>References:</p><p>Egholm, D.L. et al. (2011). Modeling the flow of glaciers in steep terrains: The integrated second‐order shallow ice approximation (iSOSIA). Journal of Geophysical Research. Vol. 116.</p><p>Herman, F. et al. (2011). Glacial hydrology and erosion patterns: A mechanism for carving glacial valleys. Earth and Planetary Science Letters. Vol. 310.</p><p>MacGregor, K.R. et al. (2000). Numerical simulations of glacial-valley longitudinal profile evolution. Geology. Vol. 28. No. 11.</p><p>Oerlemans, J. (1984). Numerical experiments on large-scale glacial erosion: Zeitschrift für Gletscherkunde und Glazialgeologie. Vol. 20.</p>

scholarly journals Why the 2014 Ludian, Yunnan, China <i>M</i><sub>s</sub> 6.5 earthquake triggered an unusually large landslide?

2015 ◽  
Vol 3 (1) ◽  
pp. 367-399 ◽  
Author(s):  
Z. F. Chang ◽  
X. L. Chen ◽  
X. W. An ◽  
J. W. Cui
Keyword(s):  
Active Fault ◽  
Rock Fractures ◽  
Catastrophic Event ◽  
Grain Sizes ◽  
Field Investigations ◽  
Rock Structure ◽  
Large Landslide ◽  
Steep Slopes ◽  
Topographic Relief ◽  
Strong Ground

Abstract. The 3 August 2014 Ludian, China Ms 6.5 earthquake has spawned a mass of severe landslides. Of them the biggest occurred at Hongshiyan near the epicenter, which has 1200 × 104 m3, clogging the Niulanjiang River, and creating a large dammed lake. Post-event field investigations yield detailed data on following aspects: rock structure of landslides, lithology, and geometry of the dam, composition and grain sizes of debris avalanches. Based on these data, this work further analyzes the geology and topography of the Hongshiyan area, and explores the mechanism for occurrence of such an unusual big landslide at this place. Our analysis suggests the following conditions are responsible for this catastrophic event: (1) during the Ms 6.5 earthquake, the special terrain and site conditions led to abnormally strong ground shake. (2) Hongshiyan lies nearby an active fault, where intense crustal deformation resulted in rock fractures and weathering. (3) Intense incision on the river increased topographic relief with steep slopes and scarps. (4) Combined structures, including unloading fissures, high-angle joints and low-angle beds along the river as well as upper-tough and lower-soft structure on the slopes. It is the joint functions of these conditions that triggered such seldom seen landslides during a moderated-sized earthquake.

scholarly journals Using GIS to detect neotectonics in the Vsetínské vrchy Mountains and in their surroundings

Geografie ◽  
2003 ◽  
Vol 108 (2) ◽  
pp. 101-114
Author(s):  
Michal Bíl
Keyword(s):  
Czech Republic ◽  
Numerical Analysis ◽  
Large Scale ◽  
Dynamic Equilibrium ◽  
Large Area ◽  
The Czech Republic ◽  
Geological Maps ◽  
Bedrock Geology ◽  
Steep Slopes ◽  
Topographic Relief

This paper discusses the advantages of GIS and numerical analysis in neotectonic studies. An accurate DEM is important for numerous geomorphic and hydrologic applications, particularly over large areas. The method is illustrated on the DEM of the Vsetínské vrchy Mountains, a 367 square km large area in the east of the Czech Republic. Comparing geological maps with large-scale morphometry shows a relationship between the rock resistance and topography. On average, higher mean elevations and steep slopes correlate well with regions of hard bedrock geology. The results together with new geological and geophysical findings show that the evolution of this part of the Outer Western Carpathian topography was proceeding continually. There is no reason to assume the presence of any periods of tectonic standstill here. The topographic relief probably has experienced the state of dynamic equilibrium.

Glacial and periglacial buzzsaws: fitting mechanisms to metaphors

2014 ◽  
Vol 81 (2) ◽  
pp. 189-192 ◽  
Author(s):  
Adrian M. Hall ◽  
Johan Kleman
Keyword(s):  
Rock Type ◽  
Causal Link ◽  
Equilibrium Line ◽  
Glacial Erosion ◽  
Ice Flow ◽  
Passive Margins ◽  
Erosion Rates ◽  
Uplift Rates ◽  
Topographic Forcing ◽  
Innate Tendency

AbstractThe buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier Equilibrium Line Altitudes (ELAs), irrespective of uplift rates, rock type or pre-existing topography. Here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and ELAs, and whether the glacial system can produce low-relief surfaces or limit summit heights. Plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited, pre-glacial relief. Summit heights may correlate with ELAs but no causal link need be implied as summit erosion rates are low, cirque headwalls may not directly abut summits and on passive margins, cirques are cut into pre-existing mountain topography. Any simple links between ELAs and glacial erosion break down on passive margins due to topographic forcing of ice-sheet growth, and to the km-scale vertical swaths through which ELAs have shifted through the Quaternary. Glaciers destroy rather than create low-relief rock surfaces through the innate tendency for ice flow to be faster, thicker and warmer along valleys. The glacial buzzsaw cuts down.

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