Glacial buzzcutting limits the height of tropical mountains

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.

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Glacial limitation of tropical mountain height

Earth Surface Dynamics ◽

10.5194/esurf-7-147-2019 ◽

2019 ◽

Vol 7 (1) ◽

pp. 147-169 ◽

Cited By ~ 5

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.

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Wetter or colder during the Last Glacial Maximum? Revisiting the pluvial lake question in southwestern North America

Quaternary Research ◽

10.1016/j.yqres.2004.07.005 ◽

2004 ◽

Vol 62 (3) ◽

pp. 280-288 ◽

Cited By ~ 44

Author(s):

Kirsten M. Menking ◽

Roger Y. Anderson ◽

Nabil G. Shafike ◽

Kamran H. Syed ◽

Bruce D. Allen

Keyword(s):

Last Glacial Maximum ◽

Late Pleistocene ◽

Annual Runoff ◽

Glacial Maximum ◽

Water Runoff ◽

Last Glacial ◽

Pleistocene Climate ◽

Surface Water Runoff ◽

The Last Glacial Maximum ◽

The Last Glacial

Well-preserved shorelines in Estancia basin and a relatively simple hydrologic setting have prompted several inquiries into the basin's hydrologic balance for the purpose of estimating regional precipitation during the late Pleistocene. Estimates have ranged from 86% to 150% of modern, the disparity largely the result of assumptions about past temperatures. In this study, we use an array of models for surface-water runoff, groundwater flow, and lake energy balance to examine previously proposed scenarios for late Pleistocene climate. Constraints imposed by geologic evidence of past lake levels indicate that precipitation for the Last Glacial Maximum (LGM) may have doubled relative to modern values during brief episodes of colder and wetter climate and that annual runoff was as much as 15% of annual precipitation during these episodes.

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Late Pleistocene climate change and Paleolithic cultural evolution in northern China: Implications from the Last Glacial Maximum

Developments in Quaternary Sciences - Late Quaternary Climate Change and Human Adaptation in Arid China ◽

10.1016/s1571-0866(07)09009-4 ◽

2007 ◽

pp. 105-128 ◽

Cited By ~ 40

Author(s):

Loukas Barton ◽

P. Jeffrey Brantingham ◽

Duxue Ji

Keyword(s):

Climate Change ◽

Last Glacial Maximum ◽

Late Pleistocene ◽

Cultural Evolution ◽

Northern China ◽

Glacial Maximum ◽

Pleistocene Climate ◽

Pleistocene Climate Change ◽

The Last Glacial Maximum ◽

The Last Glacial

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Stratigraphic constraints on late Pleistocene glacial erosion and deglaciation of the Chukchi margin, Arctic Ocean

Quaternary Research ◽

10.1016/j.yqres.2006.08.001 ◽

2007 ◽

Vol 67 (2) ◽

pp. 234-245 ◽

Cited By ~ 75

Author(s):

Leonid Polyak ◽

Dennis A. Darby ◽

Jens F. Bischof ◽

Martin Jakobsson

Keyword(s):

Arctic Ocean ◽

Younger Dryas ◽

Laurentide Ice Sheet ◽

Bering Strait ◽

Glacial Erosion ◽

Ice Shelves ◽

Sediment Stratigraphy ◽

The Last Glacial Maximum ◽

Water Depths ◽

The Last Glacial

AbstractAt least two episodes of glacial erosion of the Chukchi margin at water depths to ∼ 450 m and 750 m have been indicated by geophysical seafloor data. We examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing. Our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock. The diamictons are estimated to form during the last glacial maximum (LGM) and an earlier glacial event, possibly between OIS 4 to 5d. Both erosional events were presumably caused by the grounding of ice shelves originating from the Laurentide ice sheet. Broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor. Postglacial sedimentation evolved from iceberg-dominated environments to those controlled by sea-ice rafting and marine processes in the Holocene. A prominent minimum in planktonic foraminiferal δ18O is identified in deglacial sediments at an estimated age near 13,000 cal yr BP. This δ18O minimum, also reported elsewhere in the Amerasia Basin, is probably related to a major Laurentide meltwater pulse at the Younger Dryas onset. The Bering Strait opening is also marked in the composition of late deglacial Chukchi sediments.

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Age and development of active cryoplanation terraces in the alpine permafrost zone at Svartkampan, Jotunheimen, southern Norway

Quaternary Research ◽

10.1017/qua.2019.41 ◽

2019 ◽

Vol 92 (3) ◽

pp. 641-664 ◽

Cited By ~ 3

Author(s):

John A. Matthews ◽

Peter Wilson ◽

Stefan Winkler ◽

Richard W. Mourne ◽

Jennifer L. Hill ◽

...

Keyword(s):

Sediment Transport ◽

Groundwater Flow ◽

Age Dating ◽

Schmidt Hammer ◽

Radiocarbon Dates ◽

Exposure Age ◽

Frost Penetration ◽

Southern Norway ◽

The Last Glacial Maximum ◽

The Last Glacial

AbstractSchmidt-hammer exposure-age dating (SHD) of boulders on cryoplanation terrace treads and associated bedrock cliff faces revealed Holocene ages ranging from 0 ± 825 to 8890 ± 1185 yr. The cliffs were significantly younger than the inner treads, which tended to be younger than the outer treads. Radiocarbon dates from the regolith of 3854 to 4821 cal yr BP (2σ range) indicated maximum rates of cliff recession of ~0.1 mm/yr, which suggests the onset of terrace formation before the last glacial maximum. Age, angularity, and size of clasts, together with planation across bedrock structures and the seepage of groundwater from the cliff foot, all support a process-based conceptual model of cryoplanation terrace development in which frost weathering leads to parallel cliff recession and, hence, terrace extension. The availability of groundwater during autumn freezeback is viewed as critical for frost wedging and/or the growth of segregation ice during prolonged winter frost penetration. Permafrost promotes cryoplanation by providing an impermeable frost table beneath the active layer, focusing groundwater flow, and supplying water for sediment transport by solifluction across the tread. Snow beds are considered an effect rather than a cause of cryoplanation terraces, and cryoplanation is seen as distinct from nivation.

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How extensive was the Younger Dryas glacier advance in Austria? New insights from the Großsölk Valley

10.5194/egusphere-egu2020-19645 ◽

2020 ◽

Author(s):

Gerit E.U. Griesmeier ◽

Jürgen M. Reitner ◽

Daniel P. Le Heron

Keyword(s):

Younger Dryas ◽

Eastern Alps ◽

Crystalline Rocks ◽

Mountain Range ◽

Glacial Chronology ◽

Moraine Ridge ◽

Glacier Advance ◽

Age Constraints ◽

The Last Glacial Maximum ◽

The Last Glacial

Modern systematic studies on the record of the Alpine Lateglacial (~ 19 &#8211; 11.7 ka) are missing for the Eastern Alps east of the Hohe Tauern mountain range. In order to fill this gap, a study has been started in the Niedere Tauern mountain range, which reaches 2862 m in altitude and comprises crystalline rocks. The recently non-glaciated mountain range is famous for a glacially shaped morphology with a series of cirques. During the Last Glacial Maximum (LGM), it was part of the transection glacier complex, which covered the western and central parts of the Eastern Alps. Thus, the conditions for studying the glacial chronology after the LGM are excellent.In recent decades, three phases of glacier advances from cirques or higher altitude valleys have been distinguished within the Alpine Lateglacial, i.e. phase of ice-decay (immediately after the breakdown of the large valley glaciers like the Enns glacier), Gschnitz Stadial (correlated with the Heinrich 1 ice rafting event) and Egesen Stadial (marking the beginning of the Younger Dryas). A first step for additional paleogeographic, geochronological and palaeoglaciological studies in the Niedere Tauern is the identification and characterisation of the legacy of these three glacial phases within the Gro&#223;s&#246;lk valley.In this paper, we deal with the Egesen Stadial. New fieldwork reveals geomorphological and sedimentological evidence for glacier advances in three cirques in the Gro&#223;s&#246;lk valley. Peaks bounding these east facing cirques are at 2400-2600 m altitude. The cirques contain lateral and end moraine ridges surrounding small tongue-shaped lake basins. These up to 5 m high ridges consist of boulder-bearing sandy to gravelly diamicts, which are interpreted to have formed during discrete phases of glacier stabilisation. The observed features in the three cirques allow us to interpret the following, from south to north:1) A glacier at Lake Schimpelsee that extended down to 1930 m and which deposited three sharp crested end-moraines and one marginal moraine ridges during three stabilisation phases. 2) A similar glacier at Gr&#252;nsee that extended down to 1920 m and underwent two stabilisation phases. An end moraine ridge is not observable, because in the suspected position there is a lake today. Evidence for the second stabilisation phase is partly overprinted by a relict rock glacier. 3) At Wei&#223;ensee, large angular boulders along smoothed ridges testify to a debris-covered glacier in this area, which extended to 2000 m a.s.l.Considering the altitude of the catchment area, the eastward facing orientation, the altitude of the maximum extent of the ancient glaciers as well as the geomorphologically constrained multiphase glacier retreat, we associate these glacier advances with the Egesen Stadial. Future radionuclide work will provide better age constraints for the Gro&#223;s&#246;lk valley, extending knowledge of the W&#252;rmian Lateglacial to less investigated eastern parts of Austria.

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History and evolution of the afroalpine flora: in the footsteps of Olov Hedberg

Alpine Botany ◽

10.1007/s00035-021-00256-9 ◽

2021 ◽

Author(s):

Christian Brochmann ◽

Abel Gizaw ◽

Desalegn Chala ◽

Martha Kandziora ◽

Gerald Eilu ◽

...

Keyword(s):

Parallel Evolution ◽

Sky Islands ◽

Niche Modelling ◽

Long Distance ◽

Pleistocene Climate ◽

Modelling Studies ◽

Intrapopulation Genetic Variation ◽

New Evidence ◽

The Last Glacial Maximum ◽

The Last Glacial

AbstractThe monumental work of Olov Hedberg provided deep insights into the spectacular and fragmented tropical alpine flora of the African sky islands. Here we review recent molecular and niche modelling studies and re-examine Hedberg’s hypotheses and conclusions. Colonisation started when mountain uplift established the harsh diurnal climate with nightly frosts, accelerated throughout the last 5 Myr (Plio-Pleistocene), and resulted in a flora rich in local endemics. Recruitment was dominated by long-distance dispersals (LDDs) from seasonally cold, remote areas, mainly in Eurasia. Colonisation was only rarely followed by substantial diversification. Instead, most of the larger genera and even species colonised the afroalpine habitat multiple times independently. Conspicuous parallel evolution occurred among mountains, e.g., of gigantism in Lobelia and Dendrosenecio and dwarf shrubs in Alchemilla. Although the alpine habitat was ~ 8 times larger and the treeline was ~ 1000 m lower than today during the Last Glacial Maximum, genetic data suggest that the flora was shaped by strong intermountain isolation interrupted by rare LDDs rather than ecological connectivity. The new evidence points to a much younger and more dynamic island scenario than envisioned by Hedberg: the afroalpine flora is unsaturated and fragile, it was repeatedly disrupted by the Pleistocene climate oscillations, and it harbours taxonomic and genetic diversity that is unique but severely depauperated by frequent bottlenecks and cycles of colonisation, extinction, and recolonisation. The level of intrapopulation genetic variation is alarmingly low, and many afroalpine species may be vulnerable to extinction because of climate warming and increasing human impact.

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