DOCSLIB.ORG

Automated Approaches to Glacial Landform Mapping Tian JIA

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Automated Approaches to Glacial Landform Mapping Tian JIA [SSNI] [Tian JIA] [20382558] Supervisor: Prof. Vladimir Brusic, Dr. Ping Fu and Automated Approaches to Glacial Landform Mapping Dr. Cheng-Zhi Qin Introduction There are abundant glacial landforms in high mountain and cold regions formed by This research aims to develop a new automated approach to accurately detect and past glaciers. They are important for reconstructing the past glacier activity and map the comprehensive glacial landforms in the Tibetan Plateau, the largest climatic change. The traditional approach to mapping glacial landforms involves glaciation area outside the polar regions. The research has the following objectives. manual delineation of landform units from DEM and remotely sensed images. This • Develop an automated approach for mapping individual glacial landforms by is very time-consuming and laborious. Hence, semi-automated and automated using spatial structure information of landforms in the Tibetan Plateau. glacial landforms mapping approaches are developed for improving manual • Combine the individual glacial landforms mapping into integrate approach for mapping efficiency. However, most of the methods take insufficient account of mapping complex glacial landforms system. spatial structure information and were only applied to simple landforms in small • Apply this combined approach to map complex glacial landforms near by areas areas. of Himalayas. Glacial Landform Classification Glacial landform classification is based on alpine glacial landforms, whose classification table, schematic diagram and photographs are shown in Table 1 and Figure 1. Table 1. The classification of alpine glacial landforms that corresponding shapes are shown in Figure 1. (a) (c) Glacial Cirque (a) (b) Erosional U-shaped valley (b) (e) Source: National Park Service Glacial valley Landforms Hanging valley (c) Source: Google Earth Glacial lineation (d) (e) (d) Alpine Lateral moraine (e) Medial moraine (e) Glacial Glacial Moraine Landforms Terminal moraine (e) Depositional Source: Google Earth Source: NSIDC Landforms Recessional moraine(e) Drumlin (f) (f) (g) (h) (i) (j) Glacial boulder field (g) Outwash plain (h) Glaciofluvial Kettle (i) Kettle Landforms Source: www3.nd.edu Source: AntarcticGlaciers.org Kame (j) Source: AntarcticGlaciers.org Source: AntarcticGlaciers.org Source: (Menzies and Ross, 2020) Figure 1. The schematic diagram and photographs of glacial landforms. Glacial Landform Mapping Approaches Manual mapping Automated mapping In manual mapping of glacial landforms processes, experts define the features of Automated and semi-automated mapping techniques typically use either a pixel- target glacial landforms initially. Then, they identify the features of the landforms based or an object-based approach (Robb et al., 2015). The techniques of recent on remotely sensed sources. They use definitions from digital image processing research on the automated or semi-automated mapping approaches are shown system or a GIS (Smith et al., 2001; Greenwood and Clark, 2008). An example in Table 2. explains the process of delineating the glacial valley on Digital Elevation Model Table 2. The summary of recent semi-automated or automated mapping methods research. (DEM) (Figure 2a and 2b). They visualize the cross-section profiles of the valley to determine whether it is a glacial valley (Figure 2c) (Fu et al., 2012). Glacial landform type Author Techniques Multi-resolution segmentation Eisank et al. (2014) (a) (b) (c) algorithms (MRS) Drumlins Curvature based relief separation Yu et al. (2014) technique (CBRS) Saha et al. (2011) Object-based image analysis (OBIA) Glacial lineation Smith et al. (2016) Clustering algorithms Moraines, Flutes, Drumlins, Eskers and Robb et al. (2015) Object-based image analysis (OBIA) Sandur Figure 2. The process of determining glacial valleys by experts (Jia, 2019). Ongoing work: Data Preparation and Pre-processing for Mapping Glacial Cirques Data preparation (a) (b) (c) Satellite imagery: The outline of a Landsat 8 images Manual The features of a glacial cirque ACME mapping glacial cirque (Figure 4a, b and c) DEM: SRTM 30m Perimeter = 4298m Figure 3. The process of cirques polygon and features preparation. ACME is an ArcGIS tool named Automated Cirque Metric (d) (e) (f) Extraction developed by Spagnolo et al. in 2017. Data pre-processing Threshold Area midpoint 2D = 1399719m2 • The metrics of 11 cirque features are shown in Figure 4d, e, f, g, h and i. Surface = 1401822m2 • The metrics are extracted by summarizing the spatial pattern of the cirque. • The hypothesis is that we can use the metrics to perform automated mapping approaches. The future work will involve several stages. Z-min = 4398m Slope mean = 17° Aspect mean = 103° 1. Demonstrate the utility of the method on studying cirques by using the polygon delineation (g) (h) (i) and features extraction approach in controlling Figure 3. 2. This method will be extended to other landforms such as u-shaped valleys and moraines. Plan closure 3. We will deploy ontology design pattern (ODP) to make glacial landform definitions and deploy = 235° them with the data structure. It will be a semantic program for the automation of mapping. References NSIDC. (2020). Glacier Landforms: Moraines. Accessed: https://nsidc.org/cryosphere/glaciers/gallery/moraines.html. Z-max = 4671m Eisank, C., Smith, M., and Hillier, J. (2014). Geomorphology, 214, 452-464. Robb, C., Willis, I., Arnold, N., and Guðmundsson, S. (2015). Remote Sensing of Environment, 163, 80-90. Fu, P., Heyman, J., Hättestrand, C., Stroeven, A. P., and Harbor, J. M. (2012). Journal of Maps, 8(1), 48-55. Saha, K., Wells, N. A., and Munro-Stasiuk, M. (2011). Computers & geosciences, 37(9), 1324-1336. Greenwood, S. L., and Clark, C. D. (2008). Subglacial bedforms of the Irish ice sheet. Journal of Maps, 4(1), 332-357. Smith, M. J., Clark, C. D., and Wise, S. M. (2001). Slovak Geological Magazine, 7(3), 263-274. Jia, T. (2019). Dissertation of Bachelor of Science degree in University of Nottingham Ningbo China. Spagnolo, M., Pellitero, R., Barr, I. D., Ely, J. C., Pellicer, X. M., and Rea, B. R. (2017). Geomorphology, 278, 280-286. Figure 4. The cirque polygon visualized on Google Earth and its 11 features visualized on DEM. Menzies, J., and Ross, M. (2020). Glacial Processes and Landforms—Transport and Deposition☆. Yu, P., Eyles, N., and Sookhan, S. (2015). Geomorphology, 246, 589-601..
Load more

Recommended publications
  • Ice on the Rocks: a Glacier Shapes the Land
    Title Advance Preparation Ice on the Rocks: A Glacier Shapes the 1. Place rocks and sand in each bowl and add Land 2.5 cm of water. Allow the sand to settle, and freeze the contents solid. Later, add water until Investigative Question the bowls are nearly full and again freeze What are glaciers and how did they change the solid. These are the "glaciers" for part 1. landscape of Illinois? 2. Assemble the other materials. You may wish to do parts 1 and 3 in a laboratory setting Overview or out-of-doors because these activities are Students learn how glaciers, through abrasion, likely to be messy. transportation, and deposition, change the 3. Copy the student pages. surfaces over which they flow. Introducing the Activity Objective Hold up a square, normal-sized ice cube. Next Students conduct simulations and demonstrate to it hold up a toothpick that is as tall as the what a glacier does and how it can change the cube is thick. Ask students to picture the tallest landscape. building in Chicago, the Sears Tower. If the toothpick represents the Sears Tower, the ice Materials cube represents a glacier. The Sears Tower is Introductory activity: an ice cube and a about as tall as a glacier was thick! That was toothpick. the Wisconsinan glacier that was over 400 Part 1. For each group of five students: two meters thick and covered what is now the city plastic 1- or 2-qt. bowls; several small, of Chicago! irregularly shaped rocks or pebbles; a handful of coarse sand; a common, unglazed brick or a Procedure masonry brick (washed and cleaned); several Part 1 flat paving stones (limestone); water; access to 1.
    [Show full text]
  • Diagnosing Ice Sheet Grounding Line Stability from Landform Morphology
    Supplementary Information: Diagnosing ice sheet grounding line stability from landform morphology Lauren M. Simkins1, Sarah L. Greenwood2, John B. Anderson1 5 1 Department of Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX 77005, USA 2 Department of Geological Sciences, Stockholm University, 10691 Stockholm, Sweden *Equal contributions Correspondence to: Lauren M. Simkins ([email protected]) 1 Supplementary Methods 10 Grounding line landforms were mapped into three groups including grounding zone wedges, recessional moraines, and crevasse squeeze ridges in ArcGIS using NBP1502A and legacy multibeam data collected aboard the RVIB Nathaniel B. Palmer. Landforms displaying asymmetric morphologies and smeared surficial appearances resulting from relatively broad stoss widths (compared to lee widths) were interpreted as grounding zone wedges, whereas symmetric, quasi-linear landforms with regular spacing were interpreted as recessional moraines. Identified landforms are within fields of like 15 landforms. Within one field of recessional moraines, erratically shaped landforms with variable orientations and irregular amplitudes that are generally greater than that of the recessional moraines were interpreted as crevasse squeeze ridges. Morphometrics for grounding zone wedges and recessional moraines were generated from transects across landforms using the ‘findpeaks’ function in Matlab. Measured properties include (1) amplitude measured from landform crestlines, (2) width in the along-flow direction, (3) spacing between adjacent landform peaks, and (4) asymmetry measured as the ratio of offset 20 between the peak location and the half width point, where a landform with a value of 0 has a peak directly above the half width point and is classified as symmetric and a landform with an asymmetry of 1 has a peak furthest from the half width point and displays the most pronounced asymmetry.
    [Show full text]
  • Dating Glacial Landforms I: Archival, Incremental, Relative Dating Techniques and Age- Equivalent Stratigraphic Markers
    TREATISE ON GEOMORPHOLOGY, 2ND EDITION. Editor: Umesh Haritashya CRYOSPHERIC GEOMORPHOLOGY: Dating Glacial Landforms I: archival, incremental, relative dating techniques and age- equivalent stratigraphic markers Bethan J. Davies1* 1Centre for Quaternary Research, Department of Geography, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20 0EX *[email protected] Manuscript Code: 40019 Abstract Combining glacial geomorphology and understanding the glacial process with geochronological tools is a powerful method for understanding past ice-mass response to climate change. These data are critical if we are to comprehend ice mass response to external drivers of change and better predict future change. This chapter covers key concepts relating to the dating of glacial landforms, including absolute and relative dating techniques, direct and indirect dating, precision and accuracy, minimum and maximum ages, and quality assurance protocols. The chapter then covers the dating of glacial landforms using archival methods (documents, paintings, topographic maps, aerial photographs, satellite images), relative stratigraphies (morphostratigraphy, Schmidt hammer dating, amino acid racemization), incremental methods that mark the passage of time (lichenometry, dendroglaciology, varve records), and age-equivalent stratigraphic markers (tephrochronology, palaeomagnetism, biostratigraphy). When used together with radiometric techniques, these methods allow glacier response to climate change to be characterized across the Quaternary, with resolutions from annual to thousands of years, and timespans applicable over the last few years, decades, centuries, millennia and millions of years. All dating strategies must take place within a geomorphological and sedimentological framework that seeks to comprehend glacier processes, depositional pathways and post-depositional processes, and dating techniques must be used with knowledge of their key assumptions, best-practice guidelines and limitations.
    [Show full text]
  • A. Glacial Landform Matching B. Glacial Landform Photo & Map Exercise
    Homework #20: Glaciers Name _____________________________________ANSWERS ____ Physical Elements (Geography 1) Circle Class: 7:45 am 9:30 am 11:15 am A. GLACIAL LANDFORM MATCHING Match each of the following terms to the appropriate description below. NOTE: There are two landforms listed for which there are no matching descriptions. a. Arête f. Glacial Trough k Outwash Plain b. Cirque g Hanging Valley l. Proglacial Lake c. Finger Lake h. Horn m. Striation d. Fjord i. Kettle Lake n. Till e. Glacial Erratic j. Moraine 1. Long linear pile of glacial debris left by a retreating glacier _________J 2. Pyramid formation carved by three or more cirques _________H 3. Unsorted rock debris carried by glacial ice _________N 4. Large boulder carried by glacial ice to a location far from its parent rock _________E 5. Submerged glacial valley found along a coast _________D 6. Lake formed in depressions left by ice blocks in outwash plains _________I 7. Gouge or mark left on rock by the abrasion of debris carried by a glacier _________M 8. Valley that’s distinctly deepened, widened and straightened by glacial erosion _________F 9. Lake formed from glacial meltwater trapped by an ice dam or glacial debris _________L 10. Broad circular basin hollowed out by ice at the head of a glacial valley _________B 11. Valley that plunges into a deep trough carved out by a glacier _________G 12. Smooth flat plain formed in front of a glacier by deposition of sediment carried _________K by meltwater B. GLACIAL LANDFORM PHOTO & MAP EXERCISE Use the photos & topographic maps on the class website to answer the following questions: 1.
    [Show full text]
  • New Evidence of a Post-Laurentide Local Cirque Glacier on Mount Washington, New Hampshire Ian T
    Bates College SCARAB Honors Theses Capstone Projects Winter 12-2012 New Evidence of a Post-Laurentide Local Cirque Glacier on Mount Washington, New Hampshire Ian T. Dulin Bates College, [email protected] Brian K. Fowler [email protected] Timothy L. Cook Bates College, [email protected] Follow this and additional works at: http://scarab.bates.edu/honorstheses Recommended Citation Dulin, Ian T.; Fowler, Brian K.; and Cook, Timothy L., "New Evidence of a Post-Laurentide Local Cirque Glacier on Mount Washington, New Hampshire" (2012). Honors Theses. 20. http://scarab.bates.edu/honorstheses/20 This Open Access is brought to you for free and open access by the Capstone Projects at SCARAB. It has been accepted for inclusion in Honors Theses by an authorized administrator of SCARAB. For more information, please contact [email protected]. NEW EVIDENCE OF A POST-LAURENTIDE LOCAL CIRQUE GLACIER ON MOUNT WASHINGTON, NEW HAMPSHIRE An Honors Thesis Presented to The Faculty of the Department of Geology Bates College In partial fulfillment of the requirements for a Degree of Bachelors of Science By Ian T. Dulin Lewiston, Maine March, 2011 Acknowledgements First I’d like to thank Brian Fowler, without whom this project would not have been possible. Brian’s passion for geology really made this project enjoyable and he has been amazing to work with. I really hope we can continue to work together in the future. I’d also like to thank Tim Cook for his valuable guidance and feedback throughout the entire project. Tim’s love of geology is evident in the way he teaches.
    [Show full text]
  • Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient the Geological Society of London Books Editorial Committee
    Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient The Geological Society of London Books Editorial Committee Chief Editor Rick Law (USA) Society Books Editors Jim Griffiths (UK) Dave Hodgson (UK) Phil Leat (UK) Nick Richardson (UK) Daniela Schmidt (UK) Randell Stephenson (UK) Rob Strachan (UK) Mark Whiteman (UK) Society Books Advisors Ghulam Bhat (India) Marie-Franc¸oise Brunet (France) Anne-Christine Da Silva (Belgium) Jasper Knight (South Africa) Mario Parise (Italy) Satish-Kumar (Japan) Virginia Toy (New Zealand) Marco Vecoli (Saudi Arabia) Geological Society books refereeing procedures The Society makes every effort to ensure that the scientific and production quality of its books matches that of its journals. Since 1997, all book proposals have been refereed by specialist reviewers as well as by the Society’s Books Editorial Committee. If the referees identify weaknesses in the proposal, these must be addressed before the proposal is accepted. Once the book is accepted, the Society Book Editors ensure that the volume editors follow strict guidelines on refereeing and quality control. We insist that individual papers can only be accepted after satisfactory review by two independent referees. The questions on the review forms are similar to those for Journal of the Geological Society. The referees’ forms and comments must be available to the Society’s Book Editors on request. Although many of the books result from meetings, the editors are expected to commission papers that were not presented at the meeting to ensure that the book provides a balanced coverage of the subject. Being accepted for presentation at the meeting does not guarantee inclusion in the book.
    [Show full text]
  • Supplement of the Cryosphere, 12, 2707–2726, 2018 © Author(S) 2018
    Supplement of The Cryosphere, 12, 2707–2726, 2018 https://doi.org/10.5194/tc-12-2707-2018-supplement © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Supplement of Diagnosing ice sheet grounding line stability from landform morphology Lauren M. Simkins et al. Correspondence to: Lauren M. Simkins ([email protected]) The copyright of individual parts of the supplement might differ from the CC BY 4.0 License. S1. Supplementary Methods Grounding line landforms were mapped into three groups including grounding zone wedges, recessional moraines, and crevasse squeeze ridges in ArcGIS using NBP1502A and legacy multibeam data collected aboard the RVIB Nathaniel B. Palmer. Landforms displaying asymmetric morphologies and smeared surficial appearances resulting from relatively broad 5 stoss widths (compared to lee widths) were interpreted as grounding zone wedges, whereas symmetric, quasi-linear landforms with regular spacing were interpreted as recessional moraines. Identified landforms are within fields of like landforms. Within one field of recessional moraines, erratically shaped landforms with variable orientations and irregular amplitudes that are generally greater than that of the recessional moraines were interpreted as crevasse squeeze ridges. Morphometrics for grounding zone wedges and recessional moraines were generated from transects across landforms using 10 the ‘findpeaks’ function in Matlab. Measured properties include (1) amplitude measured from landform crestlines, (2) width in the along-flow direction, (3) spacing between adjacent landform peaks, and (4) asymmetry measured as the ratio of offset between the peak location and the half width point, where a landform with a value of 0 has a peak directly above the half width point and is classified as symmetric and a landform with an asymmetry of 1 has a peak furthest from the half width point and displays the most pronounced asymmetry.
    [Show full text]
  • The Effect of a Glaciation on East Central Sweden: Case Studies on Present Glaciers and Analyses of Landform Data
    Authors: Per Holmlund, Caroline Clason Klara Blomdahl Research 2016:21 The effect of a glaciation on East Central Sweden: case studies on present glaciers and analyses of landform data Report number: 2016:21 ISSN: 2000-0456 Available at www.stralsakerhetsmyndigheten.se SSM 2016:21 SSM perspective Background and objectives The Swedish Radiation Safety Authority reviews and assesses applica- tions for geological repositories for nuclear waste. When assessing the long term safety of the repositories it is important to consider possible future developments of climate and climate-related processes. Espe- cially the next glaciation is important for the review and assessment for the long term safety of the spent nuclear fuel repository since the presence of a thick ice sheet influences the groundwater composition, rock stresses, groundwater pressure, groundwater flow and the surface denudation. The surface denudation is dependent of the subglacial temperatures and the presence of subglacial meltwater. The Swedish Nuclear Fuel and Waste Management Company (SKB) use the Weich- selian glaciation as an analog to future glaciations. Thus, increased understanding of the last ice age will give the Swedish Radiation Safety Authority (SSM) better prerequisites to assess what impact of a future glaciation might have on a repository for spent nuclear fuel. This report compiles research conducted between 2008 and 2015 with a primary focus on 2012-2014. The primary aim of the research was to improve our understanding of processes acting underneath an ice sheet, specifically during a deglaciation. Results Based on the results of studies on present day High Alpine glaciers, the Antarctic and Greenland ice sheets, and glacial geomorphological map- ping from land and marine-based data in the Gulf of Bothnia, we have gained an insight into how future glaciations may affect the northeast coast of Uppland, eastern Sweden.
    [Show full text]
  • What Is a Glacier.Qxd
    What is a glacier? Glaciers are made up of fallen snow that, over many years, compresses into large, thickened ice masses. Glaciers form when snow remains in one location long enough to transform into ice. What makes glaciers unique is their ability to move. Due to sheer mass, glaciers flow like very slow rivers. Some glaciers are as small as football fields, while others grow to be over a hundred kilometers long. Since the mid-nineteenth century, scientists and naturalists have closely studied glaciers. In this photograph from 1894, two men approach a yawning crevasse. For safety, they use rope harnesses, attaching themselves to more stable ground further away from the crevasse. Even today, people doing fieldwork on glaciers take these precautions. Presently, glaciers occupy about 10 percent of the world's total land area, with most located in polar regions like Antarctica and Greenland. Glaciers can be thought as remnants from the last Ice Age, when ice covered nearly 32 percent of the land, and 30 percent of the oceans. An Ice Age occurs when cool temperature endure for extended periods of time, allowing polar ice to advance into lower latitudes. For example, during the last Ice Age, giant glacial ice sheets extended from the poles to cover most of Canada, all of New England, much of the upper Midwest, large areas of Alaska, most of Greenland, Iceland, Svalbard and other arctic islands, Scandinavia, much of Great Britain and Ireland, and the northwestern part of the former Soviet Union. Within the past 750,000 years, scientists know that there have been eight Ice Age cycles, separated by warmer periods called interglacial periods.
    [Show full text]
  • 1593334 B882.Pdf
    UNIVERSITY OF GOTHENBURG Department of Economy and Society, Human Geography & Department of Earth Sciences Geovetarcentrum/Earth Science Centre Detecting small-scale glacial landforms in LiDAR derived digital elevation models A case study of roches moutonnées on the Swedish west coast Gunnar Palm ISSN 1400-3821 B882 Bachelor of Science thesis Göteborg 2015 Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN Abstract The purpose of this study was to develop a method to detect and map what Sugden and John (1976) calls, “the hallmark of glacial erosion”, namely the characteristically asymmetrical rock mounds known as roches moutonnées. The roches moutonnées was to be detected in the new national elevation model provided by the Swedish mapping authority. The national elevation model was produced using an active remote sensing technique called light detection and ranging (LiDAR). LiDAR uses laser light to measure elevation and can produce very accurate digital elevation models (DEM). During the study data from the national elevation model was processed and a high resolution raster DEM was generated, processed and analyzed using geographical information systems (GIS) including ArcGIS and FME Desktop. The location of a number of roches moutonnées were marked using a GPS receiver during a field campaign. The coordinates from the GPS receiver were imported into a GIS environment in order to study the values in and around the perimeters of the surveyed roches moutonnées. The aim of this was to identify the distinctive properties of the landform, which in turn would permit a search for these properties, and thus the landform, in the entire study area.
    [Show full text]
  • Map and GIS Database of Glacial Landforms and Features Related to the Last British Ice Sheet
    Map and GIS database of glacial landforms and features related to the last British Ice Sheet CHRIS D. CLARK, DAVID J.A. EVANS, ANJANA KHATWA, TOM BRADWELL, COLM J. JORDAN, STUART H. MARSH, WISHART A. MITCHELL AND MARK D. BATEMAN Clark, C.D., Evans, D.J.A., Khatwa, A., Bradwell, T., Jordan, C.J., Marsh, S.H., Mitchell, W.A. & Bateman, M.B: Map and GIS database of glacial landforms and features related to the last British Ice Sheet. A review of the academic literature and British Geological Survey mapping is employed to produce a ‘Glacial Map’, and accompanying geographic information system (GIS) database, of features related the last (Devensian) British Ice Sheet. The Map (1:625000) is included in a folder and GIS data is freely available by web download (http://www.shef.ac.uk/geography/staff/clark_chris/britice.html). Emphasis is on information that constrains the last ice sheet. The following are included: moraines, eskers, drumlins, meltwater channels, tunnel valleys, trimlines, limit of key glacigenic deposits, glaciolacustrine deposits, ice-dammed lakes, erratic dispersal patterns, shelf-edge fans, and the Loch Lomond Readvance limit of the main ice cap. The GIS contains over 20000 features split into thematic layers (as above). Individual features are attributed such that they can be traced back to their published sources. Given that the published sources of information that underpin this work were derived by a piecemeal effort over 150 years then our main caveat is of data consistency and reliability. It is hoped that this compilation will stimulate greater scrutiny of published data, assist in palaeo-glaciological reconstructions, and facilitate use of field-evidence in numerical ice sheet modelling.
    [Show full text]
  • Landscape Developemnt of Gtneiss Terrains Under Pleistocene Ice Sheets
    Krabbendam & Bradwell – Quaternary evolution of glaciated gneiss terrains Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion Maarten Krabbendam* , Tom Bradwell British Geological Survey, Murchison House, Edinburgh EH6 3LA,United Kingdom (* Corresponding author. Tel ++44 131 6500256. Email address: [email protected]) Abstract Vast areas previously covered by Pleistocene ice sheets consist of rugged bedrock-dominated terrain of innumerable knolls and lake-filled rock basins – the ‘cnoc-and-lochan’ landscape or ‘landscape of areal scour’. These landscapes typically form on gneissose or granitic lithologies and are interpreted (1) either to be the result of strong and widespread glacial erosion over numerous glacial cycles; or (2) formed by stripping of a saprolitic weathering mantle from an older, deeply weathered landscape. We analyse bedrock structure, erosional landforms and weathering remnants and within the ‘cnoc-and- lochan’ gneiss terrain of a rough peneplain in NW Scotland and compare this with a geomorphologically similar gneiss terrain in a non-glacial, arid setting (Namaqualand, South Africa). We find that the topography of the gneiss landscapes in NW Scotland and Namaqualand closely follows the old bedrock—saprolite contact (weathering front). The roughness of the weathering front is caused by deep fracture zones providing a highly irregular surface area for weathering to proceed. The weathering front represents a significant change in bedrock physical properties. Glacial erosion (and
    [Show full text]