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 Glacial buzzcutting limits the height of tropical mountains

2018 ◽  
Author(s):  
Maxwell T. Cunningham ◽  
Colin P. Stark ◽  
Michael R. Kaplan ◽  
Joerg M. Schaefer
Keyword(s):  
Age Dating ◽  
Mountain Range ◽  
Glacial Erosion ◽  
Topographic Analysis ◽  
Tropical Mountains ◽  
Tropical Mountain ◽  
Pleistocene Climate ◽  
Cyclic Changes ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. The widespread correlation between snowline elevation and mountain height is evidence that glacial buzzcutting puts a cap on mountain growth. The match is strongest for mid-latitude ranges, where glacial erosion has persisted over Pleistocene climate cycles and tends to truncate mountain range elevation near the upper limit of the late-Pleistocene snowline. Signs of a glacial buzzsaw are weakest in tropical ranges, where glacial erosion features are sparse and generally restricted to cold periods such as the Last Glacial Maximum (LGM). Here we show that glacial erosion does indeed truncate tropical mountains, often close to the cold-phase snowline. It does so on a cyclic basis, with glacial landscapes expanding during cold periods, and contracting during largely ice-free warm periods as fluvially-driven escarpments encroach on all sides. We find evidence of this cyclicity in the perched terrain of the Chirripó massif in Costa Rica, where surface-exposure age dating and topographic analysis show that LGM denudation occurred across a glacial landscape that has shrunk during post-LGM scarp encroachment. We find a similar story in the Central Range of Taiwan, where scarp encroachment is even more severe. We deduce that, during the Pleistocene, cold-phase glacial erosion has imposed a ceiling on tropical mountain growth, and that even the archetypally steady-state landscape of Taiwan has been subject to strongly cyclic changes in erosion rate.

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 Autogenic versus allogenic controls on the evolution of a coupled fluvial megafan/mountainous catchment system: numerical modelling and comparison with the Lannemezan megafan system (Northern Pyrenees, France)

2016 ◽  
Author(s):  
Margaux Mouchené ◽  
Peter van der Beek ◽  
Sébastien Carretier ◽  
Frédéric Mouthereau
Keyword(s):  
Numerical Modelling ◽  
Temporal Variations ◽  
Tectonic Activity ◽  
Mountain Range ◽  
Stream Network ◽  
Mountainous Catchment ◽  
Isostatic Rebound ◽  
Base Level ◽  
Alluvial Terraces

Abstract. Alluvial megafans are sensitive recorders of landscape evolution, controlled by autogenic processes and allogenic forcing and influenced by the coupled dynamics of the fan with its mountainous catchment. The Lannemezan megafan in the northern Pyrenean foreland was abandoned by its mountainous feeder stream during the Quaternary and subsequently incised, leaving a flight of alluvial terraces along the stream network. We explore the relative roles of autogenic processes and external forcing in the building, abandonment and incision of a foreland megafan using numerical modelling and compare the results with the inferred evolution of the Lannemezan megafan. Autogenic processes are sufficient to explain the building of a megafan and the long-term entrenchment of its feeding river at time and space scales that match the Lannemezan setting. Climate, through temporal variations in precipitation rate, may have played a role in the episodic pattern of incision at a shorter time-scale. In contrast, base-level changes, tectonic activity in the mountain range or tilting of the foreland through flexural isostatic rebound appear unimportant.

Evolutionary conservatism will limit responses to climate change in the tropics

2021 ◽  
Vol 17 (10) ◽  
Author(s):  
Ethan B. Linck ◽  
Benjamin G. Freeman ◽  
C. Daniel Cadena ◽  
Cameron K. Ghalambor
Keyword(s):  
Thermal Tolerance ◽  
Species Turnover ◽  
Tropical Species ◽  
Evolutionary Divergence ◽  
Closely Related Species ◽  
Tropical Mountains ◽  
Low Latitudes ◽  
Parapatric Speciation ◽  
The Tropics

Rapid species turnover in tropical mountains has fascinated biologists for centuries. A popular explanation for this heightened beta diversity is that climatic stability at low latitudes promotes the evolution of narrow thermal tolerance ranges, leading to local adaptation, evolutionary divergence and parapatric speciation along elevational gradients. However, an emerging consensus from research spanning phylogenetics, biogeography and behavioural ecology is that this process rarely, if ever, occurs. Instead, closely related species typically occupy a similar elevational niche, while species with divergent elevational niches tend to be more distantly related. These results suggest populations have responded to past environmental change not by adapting and diverging in place, but instead by shifting their distributions to tightly track climate over time. We argue that tropical species are likely to respond similarly to ongoing and future climate warming, an inference supported by evidence from recent range shifts. In the absence of widespread in situ adaptation to new climate regimes by tropical taxa, conservation planning should prioritize protecting large swaths of habitat to facilitate movement.

Estimating the snow-rain transition zone in a semi-arid Andean catchment

2021 ◽  
Author(s):  
Simone Schauwecker ◽  
Gabriel Palma ◽  
Shelley MacDonell ◽  
Katerina Goubanova
Keyword(s):  
Transition Zone ◽  
Early Warning Systems ◽  
Mountain Range ◽  
Arid Environments ◽  
Local Conditions ◽  
The Andes ◽  
Snow Line ◽  
Snow Cover Extent ◽  
Semi Arid ◽  
Precipitation Events

<p>The height of the snow-rain transition during infrequent but high impact precipitation events, closely related to the 0⁰C-isotherm, is a crucial variable for snow cover extent, high discharge flows and flash floods in semi-arid northern Chile. Estimations of the snow-rain transition zone and its past and future changes are therefore fundamental for adaptation strategies and might eventually serve to develop early warning systems in this region. However, there are important challenges that hinder the assessment of the snow-rain transition zone in semi-arid environments and little is known about past and future changes under different global warming scenarios. For example, there are few radiosonde observations along the Andes and most weather stations are located in valley bottoms, influenced by local conditions and the assumption of free-air temperature lapse rates contributes to the uncertainty. We combine different data sets to estimate the past snow-rain transition zone of our study site, the semi-arid Elqui river catchment. Pictures of the snow line after precipitation events - available from social networks - are used to visually estimate the snow line elevation. These values are in high agreement with vertically extrapolated temperature from meteorological stations. Furthermore, we identified considerable biases between the extrapolated 0⁰C-isotherm from meteorological stations and ERA5 reanalysis data. These large biases are probably due to the lowering of the freezing level over complex terrain and need further analysis. Our results contribute to an improved understanding of the snow-rain transition in this region, but also serve to derive a climatology of this key variable along the Andes mountain range, needed for future projections.</p>

scholarly journals Mass Balance of “Vesper” Glacier, Washington, U.S.A.

1981 ◽  
Vol 27 (96) ◽  
pp. 271-282 ◽  
Author(s):  
David P. Dethier ◽  
Jan E. Frederick
Keyword(s):  
Nineteenth Century ◽  
Mass Balance ◽  
Cascade Range ◽  
Equilibrium Line ◽  
Equilibrium Line Altitude ◽  
Climatic Fluctuations ◽  
The North ◽  
Snow Line ◽  
The Relationship ◽  
Geologic Data

AbstractDuring 1974–75 glaciologic and geologic studies were conducted on a small (0.17 km2) avalanche-nourished glacier in the North Cascade Range of Washington. The approximate equilibrium-line altitude (ELA) for this ice body, informally called “Vesper” glacier, lies at 1475 m, some 300 m below the regional ELA value. Estimated annual accumulation was 6 100±675 mm during the two years of study; 15 to 30% of this flux resulted from avalanche and wind–transported snow. Average annual ablation during the period was 5 350 mm, giving a total net balance of + 1 600 mm for the two-year study period. “Vesper” glacier persists well below the regional snow-line because of excessive local precipitation, substantial avalanche contributions, and a favourable north-facing aspect.Neoglacial moraines indicate that maximum ELA lowering in this period was approximately 165 m and occurred prior to a.d. 1670. Minor re-advances occurred during the nineteenth century. These reconnaissance measurements are consistent with the sparse geologic data reported from other glaciers in the Cascade Range. While the relationship between regional lowering of snow-line and avalanche activity is uncertain at present, these data suggest that avalanche-nourished glaciers provide a useful record of climatic fluctuations.

scholarly journals Non-Synchronous Response Of Rabots Glaciar and Storglaciaren To Recent Climatic Change

1990 ◽  
Vol 14 ◽  
pp. 331-332
Author(s):  
Keith A. Brugger
Keyword(s):  
Steady State ◽  
Response Time ◽  
Mass Balance ◽  
Climatic Change ◽  
Regional Climate ◽  
Wave Model ◽  
Equilibrium Line Altitude ◽  
Local Climate ◽  
Climatic Oscillations ◽  
Basin Topography

Rabots glaciär and Storglaciären are small valley glaciers located in the Kebnekaise massif of northern Sweden. Rabots glaciär flows west from the summit of Kebnekaise (2114 m) and Storglaciären flows east; thus regional climate affecting the glaciers is the same. The glaciers are of comparable size and geometry, although differences exist in the variation of ice thickness and the subglacial bedrock topography within the respective basins. The thickness of Rabots glaciär appears to be relatively uniform over much of its length and its bed smooth. The bed over which Storglaciären flows is characterized by a “riegel and basin” topography and ice thicknesses vary accordingly. Advance and retreat of the glaciers during the last 100 years has been documented by historical records and photographs, measurements of ice retreats, and detailed glacial and geological studies. Both advanced to their maximum 20th century extents around 1916. In their subsequent retreat, Rabots glaciär has lagged behind Storglaciären by 10 years. Mass-balance studies for the years 1981–87 suggest that while the “local” climate for each glacier is slightly different (in terms of the magnitude of acumulation and ablation), variations in local climate are synchronous. Non-synchronous response of the glaciers is therefore attributed to differences in glacier dynamics, which are quite apparent when velocity profiles are compared. Ice velocities on Rabots glaciär vary little from an average of −7.5 m/yr, resulting in a longitudinal strain rate, r, of about 6 × 10−3yr −1. In contrast, values for r on Storglaciären are as high as 2.5 × 10−2 yr−1 owing to greater ice velocities and variation in ice velocity. Since the response time of a glacier is proportional to 1/r, the lower strain rates found on Rabots glaciär probably account for its more sluggish retreat. A simple, non-diffusive, kinematic wave model is used to analyze the response of the glaciers to a step-like perturbation in mass balance. This model predicts that the response time of Storglaciären is on the order of 30 years and that a new steady-state profile would be attained in about 50 years. The predicted response time of Rabots glaciär is about 75 years, its new steady-state profile being reached after more than 100 years. More accurate analyses of each glacier's response to climatic change use a time-dependent numerical model which includes the effects of diffusion. The climatic forcing in these modelling efforts is represented by the changes in mass balance resulting from changes in the equilibrium line altitude (ELA). ELAs can be correlated to regional meteorological variables which in turn are used to create a “synthetic” record of ELA variations where necessary. Therefore climatic oscillations since the turn of the century can be simulated by the appropriate changes in ELA. Using synchronous variations of ELAs and their 1916 profiles as datum states, the modeled behavior of Rabots glaciär and Storglaciären shows that: (a) the rates of ice retreat for each glacier are in reasonable agreement with those observed; and (b) Rabots glaciär took slightly longer than Storglaciären to react to the slight warming that occurred shortly after their 1916 advance.

scholarly journals Ice-Sheet Erosion—A Result of Maximum Conditions?

1979 ◽  
Vol 23 (89) ◽  
pp. 402-404 ◽  
Author(s):  
D. E. Sugden
Keyword(s):  
Steady State ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Gradual Transition ◽  
Glacial Erosion ◽  
Mountain Glaciers ◽  
State Models ◽  
Ice Sheet Erosion ◽  
The Relationship ◽  
Sheet Erosion

Abstract Understanding the relationship between the morphology of former ice-sheet beds and glaciological processes is handicapped by the difficulty of establishing which stage of a cycle of ice-sheet growth and decay is responsible for most erosion. Discussions at this conference and in the literature display a variety of opinions, some favouring periods of ice-sheet build up, others periods of fluctuations, and still others steady-state maximum conditions. Here it is suggested that there is geomorphological evidence which points to the dominance of maximum conditions. Along the eastern margins of the Laurentide and Greenland ice sheets there is a sharp discontinuity between Alpine relief which stood above the ice-sheet surface at the maximum and plateau scenery which was covered by the ice sheet. Often the two types of relief are adjacent and yet separated by an altitudinal difference of only 100–200 m. The existence of an abrupt rather than gradual transition from one relief type to the other suggests that most glacial sculpture must have taken place while the ice sheet was at its maximum extent. In other geomorphological situations where high mountains were submerged by ice sheets, the major erosional landforms are frequently found to relate to ice sheets rather than to local mountain glaciers, again suggesting the dominance of erosion during full ice-sheet conditions. Finally, the identification of patterns of glacial erosion on an ice-sheet scale in North America and Greenland points to erosion when the ice sheets were fully expanded, rather than to the variable flow conditions associated with growth or decay. If ice-sheet erosion is accepted as being a result of maximum conditions, then it places certain constraints on glacial theory, for example the need to develop theories of glacial erosion which apply beneath ice thicknesses of several thousand metres. It also suggests that the use of steady-state models of ice sheets is likely to be a profitable way of relating glaciological processes to the morphology of former ice-sheet beds.

scholarly journals Glacier Fluctuations and Climate in the Cordillera Blanca, Peru

1990 ◽  
Vol 14 ◽  
pp. 136-140 ◽  
Author(s):  
Georg Kaser ◽  
Alcides Ames ◽  
Marino Zamora
Keyword(s):  
Seasonal Temperature ◽  
Wet Season ◽  
Equilibrium Line Altitude ◽  
Cordillera Blanca ◽  
Covered Area ◽  
Recession Rates ◽  
Tropical Areas ◽  
Precipitation Records ◽  
The Tropics

With a total of 723 km2 of glaciers (1970) the Cordillera Blanca includes the largest glacier-covered area in the tropics. The climate is characterized by relatively large daily and small seasonal temperature variations as well as by a distinct succession between a dry (May–September) and a wet season (October–April). Since the early 1970s an ablation stake network has been installed on the tongues of the glaciers Uruashraju and Yanamarey. The determination of the equilibrium-line altitude at each end of a wet season was possible, showing a fair correlation with temperature, but not with the precipitation records of the nearby climatological station Querococha. Mean ablation rates at the lowest parts of the glacier tongues are markedly higher during the wet season than during the dry season. Reasons are presumably to be found in the seasonal variation of cloudiness and air moisture rates. Terminus variations of four glaciers in the Cordillera Blanca have been monitored since the early seventies, earlier positions are reconstructed back to 1948 by vertical air photographs. For the glaciers Uruashraju and Yanamarey the terminus positions of 1939 are known from an early map. The general retreat of glaciers in the Cordillera Blanca during the last five decades correlates with the global attitude of glaciers and especially with the attitude of glaciers in other tropical areas. Decreased recession rates with minor advances (1974–79 and 1985–86) are accompanied by lower annual temperatures and preceded and accompanied by years with relatively high annual precipitation sums.

scholarly journals How steady are steady-state mountain belts? A reexamination of the Olympic Mountains (Washington state, USA)

2019 ◽  
Vol 7 (1) ◽  
pp. 275-299 ◽  
Author(s):  
Lorenz Michel ◽  
Christoph Glotzbach ◽  
Sarah Falkowski ◽  
Byron A. Adams ◽  
Todd A. Ehlers
Keyword(s):  
Steady State ◽  
Washington State ◽  
Cascadia Subduction Zone ◽  
Mountain Range ◽  
Accretionary Wedge ◽  
Pleistocene Glaciation ◽  
Kinematic Modeling ◽  
Olympic Mountains ◽  
Mountain Belts ◽  
Exhumation Rates

Abstract. The Olympic Mountains of Washington state (USA) represent the aerially exposed accretionary wedge of the Cascadia Subduction Zone and are thought to be in flux steady state, whereby the mass outflux (denudation) and influx (tectonic accretion) into the mountain range are balanced. We use a multi-method approach to investigate how temporal variations in the influx and outflux could affect previous interpretations of flux steady state. This includes the analysis of published and new thermochronometric ages for (U–Th) ∕ He dating of apatite and zircon (AHe and ZHe, respectively), fission-track dating of apatite and zircon (AFT and ZFT, respectively), 1-D thermo-kinematic modeling of thermochronometric data, and independent estimates of outflux and influx. In total, we present 61 new AHe, ZHe, AFT, and ZFT thermochronometric ages from 21 new samples. AHe ages are generally young (< 4 Ma), and, in some samples, AFT ages (5–8 Ma) overlap ZHe ages (7–9 Ma) within uncertainties. Thermo-kinematic modeling shows that exhumation rates are temporally variable, with rates decreasing from > 2 to < 0.3 km Myr−1 around 5–7 Ma. With the onset of Plio–Pleistocene glaciation, exhumation rates increased to values > 1 km Myr−1. This demonstrates that the material outflux varies through time, requiring a commensurate variation in influx to maintain flux steady state. Evaluation of the offshore and onshore sediment record shows that the material influx is also variable through time and that the amount of accreted sediment in the wedge is spatially variable. This qualitatively suggests that significant perturbations of steady state occur on shorter timescales (105–106 years), like those created by Plio–Pleistocene glaciation. Our quantitative assessment of influx and outflux indicates that the Olympic Mountains could be in flux steady state on long timescales (107 years).

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