Post-Younger Dryas deglaciation of the Greenland western margin as revealed by spatial analysis of lakes

Lake shapes and their spatial distribution are important geomorphological indicators in previously glaciated areas. Their shapes are influenced by the underlying geological structure and processes of glacial sediment deposition or erosion. Since these processes act on large areas, distribution of lakes can reflect the intensity of glacial erosional/depositional processes and their spatial extent. Landsat imagery was used to extract lake outlines from a selected pilot-study area on the widest ice-free coastal margin of the south-western Greenland north of Kangerlussuaq. Analysis included image classification and spatial analysis of lakes with elevation data using geographic information system (GIS) tools. A morphometric index was applied to extract kettle lakes as indicators of a specific glacial process – ice stagnation. Analysis of their spatial distribution helped in the reconstruction of glacial dynamics in formerly glaciated terrain. Our results show that spatial lake distribution combined with elevation analysis can be used to identify zones of glacial erosion and deposition. The highest concentrations of lakes within the study area occupy the elevation range between 164 and 361 m above sea level (a.s.l.). This zone can be identified as an area where intensive glacial erosion took place in the past. The widespread distribution of modeled kettle lake features within the same elevation range and across the study area suggests that the last deglaciation process was accompanied by abandonment of blocks of stagnant ice. This conclusion is supported by surface exposure ages obtained in the same study area and published elsewhere. Copyright © 2009 John Wiley & Sons, Ltd

Preliminary ¹⁰Be chronology for the last deglaciation of the western margin of the Greenland Ice Sheet

The now acknowledged thinning of the Greenland Ice Sheet raises concerns about its potential contribution to future sea level rise. In order to appreciate the full extent of its contribution to sea level rise, reconstruction of the ice sheet's most recent last deglaciation could provide key information on the timing and the height of the ice sheet at a time of rapid climate readjustment. We measured 10Be concentrations in 12 samples collected along longitudinal and altitudinal transects from Sisimiut to within 10 km of the Isunguata Sermia Glacier ice margin on the western coast of Greenland. Along the longitudinal transect, we collected three perched boulders and two bedrocks. In addition, we sampled seven perched boulders along a vertical transect in a valley within 10 km of the Isunguata Sermia Glacier ice margin. Our pilot dataset constrains the height of the ice sheet during the Last Glacial Maximum (LGM) between 500 m and 840 m (including the 120 m relative sea level depression at the time of the LGM, 21 ka BP). From the transect we estimate the thinning of the ice sheet at the end of the deglaciation between 12.3 ± 1.5 10Be ka (n = 2) and 8.3 ± 1.2 10Be ka (n = 3) to be ∼6 cm a−1 over this time period. Direct dating of the retreat of the western margin of the Greenland Ice Sheet has the potential to better constrain the retreat rate of the ice margin, the thickness of the former ice sheet as well as its response to climate change. Copyright © 2008 John Wiley & Sons

Expression of the younger Dryas cold event in the Carpathian Mountains, Ukraine?

Past glacial activity in the Ukrainian Carpathian Mountains is characterized by cirques, glacial valleys and moraine ridges at altitudes between 1350 and 1850 m a.s.l. Although the geomorphology of this area was extensively studied, the deposition time of these glacial forms, and specifically the moraines was never determined. We surveyed and mapped the geomorphology of the Pozhezhevs’ka glacial Valley, which is part of the Charnogora Ridge. We used surface exposure dating and developed a data base of this area using remote sensing and Geographic Information System to understand the timing and nature of glacial event in the eastern Carpathian Mountains. Well-developed continuous lateral-frontal moraines cross the valley floor at ∼1400 m a.s.l. Ten sandstone boulders were sampled from one of these to determine the deposition time of the moraine. Samples were prepared at the Glasgow University Cosmogenic Nuclide Laboratory and analyzed at the SUERC AMS Laboratory. Surface exposure ages were calculated using the CRONUS-Earth online 10Be exposure age calculator. Our exposure ages for nine samples (UKR-2 to UKR-10) range from 11.0 ± 0.4 10Be ka to 14.5 ± 0.5 10Be ka. One sample (UKR-1) produced no current and thus no exposure age is available. The mean deposition time for the moraine ranges from 12.4 ± 0.3 to 12.9 ± 0.3 10Be ka, depending on choice of surface erosion and snow cover. These results provide the first direct indication, using surface exposure dating, of a possible glacier response in the Ukrainian Carpathian Mountains to a cold event contemporary with the Younger Dryas (YD). Together with exposure ages from other mountain ranges across Europe, the new data provide direct chronological evidence for a widespread expression of the YD cold event outside the main ice margin limits left by the former Scandinavian Ice Sheet

Evaluation of global digital elevation model for flood risk management in Perlis

In flood modelling process, Digital Elevation Models (DEMs) is a valuable tool in topographic parameterization of hydrological models. The release of the free-of-charge satellite based DEMs such as SRTM and ASTER prompted the accurate flood modelling process especially to propose flood mitigation in the Perlis region. In this research, the accuracy of SRTM DEM of spatial resolution 1 arc-sec and 3 arc-sec, as well as ASTER DEM are evaluated. The reference levels produced from GNSS observation and Earth Gravitational Model 1996 (EGM96), as well as local mean sea level are used to analyse the vertical accuracy of each GDEMs in Perlis, Malaysia. The total of 38 Benchmark (BM) and Standard Benchmark (SBM) around the Perlis region were observed by GNSS using static method and processed using TOPCON Tool software. A comparison with the local mean sea level height indicated that SRTM 1″ is the much greater absolute vertical accuracy with an RMSE of ±3.752 m and continued by SRTM 3″ and ASTER GDEMs where the obtained accuracy was ±4.100 and ±5.647 m, respectively. Also, by using orthometric height form the GNSS and EGM96 as reference elevation, the obtained accuracy was ±3.220, ±3.597, and ±5.832 m for SRTM 1″, SRTM 3″ and ASTER, respectively. Statistical results have also shown that SRTM 1″ has a good correlation with Hmsl and HGNSS where both correlations values are 0.9925, while the SRTM 3″ and ASTER show the correlation of 0.9873 and 0.9375