scholarly journals Structural characterisation, internal deformation, and kinematics of an active deep-seated rock slide in a valley glacier retreat area

2021 ◽  
Vol 286 ◽  
pp. 106048
Author(s):  
Christina Rechberger ◽  
Christine Fey ◽  
Christian Zangerl
2017 ◽  
Vol 63 (239) ◽  
pp. 450-463 ◽  
Author(s):  
LAURA I. THOMSON ◽  
LUKE COPLAND

ABSTRACTAnnual and seasonal surface velocities measured continuously from 1960 to 1970 at White Glacier, a 14 km long polythermal valley glacier spanning ~100–1800 m a.s.l., provide the most comprehensive early record of ice dynamics in the Canadian Arctic. Through comparison with differential GPS-derived velocity data spanning 2012–16, we find reductions in mean annual velocity by 31 and 38% at lower elevations (600 and 400 m a.s.l.). These are associated with decreased internal ice deformation due to ice thinning and reduced basal motion likely due to increased hydraulic efficiency in recent years. At higher elevation (~850 m a.s.l.) there is no detectable change in annual velocity and the expected decrease in internal deformation rates due to ice thinning is offset by increased basal motion in both summer and winter, likely attributable to supraglacial melt accessing a still inefficient subglacial drainage system. Decreases in mass flux at lower elevations since the 1960s cannot explain the observed elevation loss of ~20 m, meaning that ice thinning along the glacier trunk is primarily a function of downwasting rather than changing ice dynamics. The current response of the glacier exemplifies steady thinning, velocity slowdown and upstream retreat of the ELA but, because the glacier has an unstable geometry with considerable mass in the 1300–1500 m elevation range, a retreat of the ELA to >1300 plausible within 25–40 years, could trigger runaway wastage.


2008 ◽  
Vol 54 (184) ◽  
pp. 145-156 ◽  
Author(s):  
E.C. King ◽  
A.M. Smith ◽  
T. Murray ◽  
G.W. Stuart

AbstractWe conducted a seismic and radar survey of the central part of midtre Lovénbreen, a small, polythermal valley glacier in Svalbard. We determined the physical properties of the material beneath the glacier by measuring the reflection coefficient of the bed by comparing the energy of the primary and multiple reflections, and deriving the acoustic impedance. By making reasonable assumptions about the properties of the basal ice, we determined the acoustic impedance of the bed material as (6.78 ± 1.53) × 106 kg m−2 s−1. We interpret the material beneath the glacier to be permafrost with up to 50% ice, and we speculate that the material may be frozen talus similar to a deposit observed directly by others beneath another Svalbard glacier. The implication for midtre Lovénbreen is that the basal material beneath the present glacier is not able to support fast flow. We conclude that midtre Lovénbreen has most likely had limited capability for faster flow in the past, with motion dominated by internal deformation. Midtre Lovénbreen is used as a ‘study glacier’ for the scientific community in Svalbard, and a large number of studies have been based there. Our results show that it cannot be used as an analogue for larger glaciers in Svalbard, having distinct basal boundary conditions.


JOKULL ◽  
2020 ◽  
Vol 69 ◽  
pp. 129-136
Author(s):  
Hrafnhildur Hannesdóttir

Glacier variations 1930–1970, 1970–1995, 1995–2017 and 2017–2018 The Icelandic Glaciological Society received reports on 46 measurements sites of glacier front variations in the autumn of 2018. Glacier retreat was observed at 33 survey sites whereas advances where reported from 5 sites, and 4 showed no signs of change. Snow covered glacier margins, bad weather or floating icebergs in the proglacial lakes prevented measurement at a few sites. One new site was added to the network, the western part of Þórisjökull.


1983 ◽  
Vol 29 (103) ◽  
pp. 515-520
Author(s):  
J. N. J. Visser

Abstract The upper part of a Permo-Carboniferous glacial valley fill along the northern margin of the Karoo Basin includes glacio-lacustrine sediments. During the last glacier advance into the lake, a bedded heterogeneous diamictite facies was deposited and, on glacier retreat, a sequence of deformed siltstones with diamictite lenses and sandstone beds, varved shale and rhythmite shale was laid down. Black carbonaceous mud was deposited during the subsequent marine transgression. According to varve counts, the glacier receded from the valley over a period of 500 to 1 000 years and it is concluded that the overall ice-retreat rate during the Permo-Carboniferous deglaciation was relatively high.


1984 ◽  
Vol 21 (10) ◽  
pp. 1082-1097 ◽  
Author(s):  
S. L. Fumerton ◽  
M. R. Stauffer ◽  
J. F. Lewry

The Early Proterozoic Wathaman batholith, in northern Saskatchewan and Manitoba, is a 900 km long, megacrystic granite–granodiorite intrusion that straddles the junction between ensialic miogeoclinal and probably ensimatic eugeoclinal–island-arc terranes of the "Trans-Hudson Orogen," of the western Churchill Province. Although the largest Precambrian batholith known, it is, apart from marginal complexities, remarkably homogeneous throughout and, unlike comparably sized and situated Phanerozoic batholiths, shows no evidence of multiple intrusion, nor does it have comagmatic early mafic phases. However, it may be considered as just one phase of a larger batholithic belt that also includes numerous smaller plutons. Taken as a whole the composite batholithic belt is similar in many aspects to Mesozoic Pacific rim batholithic belts, and like them probably was emplaced during plate collision.The batholith is affected by pervasive internal deformation, is bounded on the northwest by major blastomylonite zones, and is transected internally by splaying shear zones. It is a mid- to late-synkinematic Hudsonian intrusion, emplaced within a markedly compressional, crustal regime. On the basis of petrological, geochemical, and isotopic criteria the batholith is an "I-type" intrusion, but the origin of the magma and the emplacement mechanisms are still unresolved problems.


Sign in / Sign up

Export Citation Format

Share Document