scholarly journals The enigma of relict large sorted stone stripes in the tropical Ethiopian Highlands

2021 ◽  
Vol 9 (2) ◽  
pp. 145-166
Author(s):  
Alexander R. Groos ◽  
Janik Niederhauser ◽  
Luise Wraase ◽  
Falk Hänsel ◽  
Thomas Nauss ◽  
...  
Keyword(s):  
Ground Temperature ◽  
Polar Regions ◽  
Freezing And Thawing ◽  
Patterned Ground ◽  
Independent Evidence ◽  
Ethiopian Highlands ◽  
Geomorphological Mapping ◽  
Exposure Dating ◽  
Aerial Photogrammetry ◽  
Geomorphic Features

Abstract. Large forms of sorted patterned ground belong to the most prominent geomorphic features of periglacial and permafrost environments of the mid-latitudes and polar regions, but they were hitherto unknown in the tropics. Here, we report on relict large sorted stone stripes (up to 1000 m long, 15 m wide, and 2 m deep) on the ca. 4000 m high central Sanetti Plateau of the tropical Bale Mountains in the southern Ethiopian Highlands. These geomorphic features are enigmatic since forms of patterned ground exceeding several metres are commonly associated with distinct seasonal ground temperatures, oscillating around 0 ∘C. To systematically investigate present frost phenomena and relict periglacial landforms in the Bale Mountains, we conducted extensive geomorphological mapping. The sorted stone stripes were studied in more detail by applying aerial photogrammetry, ground-penetrating radar measurements, and 36Cl surface exposure dating. In addition, we installed ground temperature data loggers between 3877 and 4377 m to analyse present frost occurrence and seasonal ground temperature variations. Superficial nocturnal ground frost was measured at 35–90 d per year, but the ground beneath the upper few centimetres remains unfrozen the entire year. Seasonal frost occurrence would require a mean annual ground temperature depression of about 11 ∘C, corresponding to an air temperature decrease of about 6–8 ∘C (relative to today) as inferred from a simple statistical ground temperature model experiment. Our results suggest the formation of the large sorted stone stripes under past periglacial conditions related to lateral and vertical frost sorting in the course of cyclic freezing and thawing of the ground. It is likely that the stone stripes formed either in proximity to a former ice cap on the Sanetti Plateau over the last glacial period due to seasonal frost heave and sorting or they developed over multiple cold phases during the Pleistocene. Although certain aspects of the genesis of the large sorted stone stripes remain unresolved, the presence of these geomorphic features provides independent evidence besides glacial landforms for unprecedented palaeoclimatic and palaeoenvironmental changes in the tropical Bale Mountains during the (Late) Pleistocene.

scholarly journals Implications of present ground temperatures and relict stone stripes in the Ethiopian Highlands for the palaeoclimate of the tropics

2020 ◽  
Author(s):  
Alexander R. Groos ◽  
Janik Niederhauser ◽  
Luise Wraase ◽  
Falk Hänsel ◽  
Thomas Nauss ◽  
...  
Keyword(s):  
Air Temperature ◽  
Ground Temperature ◽  
Seasonal Temperature ◽  
Ethiopian Highlands ◽  
Last Glacial ◽  
Exposure Dating ◽  
Ice Cap ◽  
The Tropics ◽  
Temperature Depression ◽  
The Last Glacial

Abstract. Large sorted patterned grounds are the most prominent features of periglacial and permafrost environments of the mid and high latitudes, but have not yet been verified for the tropics. Here, we report on relict large sorted polygons (up to 8 m in diameter) and large sorted stone stripes (up to 1000 m long, 15 m wide, and 2 m deep) on the ~ 4000 m high Sanetti Plateau in the Bale Mountains, southern Ethiopian Highlands. For a systematic investigation of past and present frost-related processes and landforms in the Bale Mountains, we conducted geomorphological mapping both in the field and on satellite images. The sorted stone stripes were studied in more detail by applying aerial photogrammetry, ground-penetrating radar measurements, and 36Cl surface exposure dating. In addition, we installed 29 ground temperature data loggers between 3493 and 4377 m to analyse present frost occurrence and seasonal temperature variations from 2017 to 2020. Finally, we ran a simple experiment and combined recent ground temperature measurements with meteorological data in a statistical model to assess the air temperature depression needed for the past formation of deep seasonal frost and cyclic freezing and thawing on the plateau. Our results show that relict and modern periglacial landforms are common in the Bale Mountains. Nocturnal superficial ground frost on the plateau occurs at 35–90 days per year, but the mean annual ground temperature (~ 11 °C) is far off from seasonal or permanent frost conditions. The modelling experiment suggests a minimum air temperature depression on the plateau of 7.6 ± 1.3 °C for the emergence of several decimetre deep seasonal frost. The stone stripes probably formed under periglacial conditions in proximity of a palaeo ice cap on the plateau during the coldest period(s) of the last glacial cycle. We hypothesise that the slightly inclined and unglaciated areas of the plateau, the coexistence of regolith and large blocks, the occurrence of deep seasonal frost, as well as relatively dry conditions beyond the ice cap provided ideal conditions for frost heave and sorting and the formation of large sorted patterned grounds. The presence of these landforms and the associated air temperature depression provide further evidence for an amplified cooling of high tropical mountains during the last glacial period that is yet not well captured in global climate models.

scholarly journals Applying floodplain geomorphology to flood management (The Lower Vistula River upstream from Plock, Poland)

2020 ◽  
Vol 12 (1) ◽  
pp. 1003-1016
Author(s):  
Grzegorz Wierzbicki ◽  
Piotr Ostrowski ◽  
Tomasz Falkowski
Keyword(s):  
Flood Hazard ◽  
Field Work ◽  
Flood Management ◽  
Erosion And Deposition ◽  
Geomorphological Mapping ◽  
Vistula River ◽  
Overbank Flow ◽  
Geomorphic Features ◽  
Gradient Condition ◽  
Topographical Maps

AbstractUsing remote sensing extended on geological and topographical maps and verified by the field work, we present the flood management and study the geomorphic features of the floodplain of a large, sand bed, untrained but embanked river in order to determine the flood hazard and to predict future flood scenarios. In geomorphological mapping, we focus on the landforms: crevasse channels and splays, flood basin, chute channels, side arms, floodplain channels, dunes and fields of aeolian sand. We base the flood risk assessment on consultations with environmental engineers who design new technical structures that control inundation (cut-off walls and lattice levees). We describe a levee breach as a result of piping (inner erosion) in a high hydraulic gradient condition and its effect (scour hole) as an erosional landform consistent with the repetitive pattern of erosion and deposition formed by an overbank flow on a floodplain. We reveal an existence of homogenous morphodynamic reaches in the river valley.

scholarly journals Geomorphological mapping based on DEMs and GIS: A review

2019 ◽  
Vol 1 ◽  
pp. 1-1
Author(s):  
Takashi Oguchi
Keyword(s):  
Remote Sensing ◽  
Laser Scanning ◽  
Aerial Photographs ◽  
Topographic Maps ◽  
Formation Processes ◽  
Geomorphological Mapping ◽  
Topographic Data ◽  
Aerial Photogrammetry ◽  
Landform Classification ◽  
Shape Characteristics

<p><strong>Abstract.</strong> Geomorphology is a scientific discipline dealing with the characteristics, origin, and evolution of landforms. It utilizes topographic data such as spot height information, contour lines on topographic maps, and DEMs (Digital Elevation Models). Topographic data were traditionally obtained by ground surveying, but introduction of aerial photogrammetry in the early 20th century enabled more efficient data acquisition based on remote sensing. In recent years, active remote sensing methods including airborne and terrestrial laser scanning and applications of satellite radar have also been employed, and aerial photogrammetry has become easier and popular thanks to drones and a new photogrammetric method, SfM (Structure from Motion). The resultant topographic data especially raster DEMs are combined with GIS (Geographic Information Systems) to obtain derivatives such as slope and aspect as well as to conduct efficient geomorphological mapping. Resultant maps can depict various topographic characteristics based on surface height and DEM derivatives, and applications of advanced algorithms and some heuristic reasoning permit semi-automated landform classification. This quantitative approach differs from traditional and more qualitative methods to produce landform classification maps using visual interpretation of analogue aerial photographs and topographic maps as well as field observations.</p><p>For scientific purposes, landforms need to be classified based on not only shape characteristics but also formation processes and ages. Among them, DEMs only represent shape characteristics, and understanding formation processes and ages usually require other data such as properties of surficial deposits observed in the field. However, numerous geomorphological studies indicate relationships between shapes and forming-processes of landforms, and even ages of landforms affect shapes such as a wider distribution of dissected elements within older landforms. Recent introduction of artificial intelligence in geomorphology including machine learning and deep learning may permit us to better understand the relationships of shapes with processes and ages. Establishing such relationships, however, is still highly challenging, and at this moment most geomorphologists think landform classification maps based on the traditional methods are more usable than those from the DEM-based methods. Nevertheless, researchers of some other fields such as civil engineering more appreciate the DEM-based methods because they can be conducted without deep geomorphological knowledge. Therefore, the methods should be developed for interdisciplinary understanding. This paper reviews and discusses such complex situations of geomorphological mapping today in relation to historical development of methodology.</p>

scholarly journals Morphological evidence for geologically young thaw of ice on Mars: A review of recent studies using high-resolution imaging data

2013 ◽  
Vol 37 (3) ◽  
pp. 289-324 ◽  
Author(s):  
M.R. Balme ◽  
C.J. Gallagher ◽  
E. Hauber
Keyword(s):  
Liquid Water ◽  
Morphological Evidence ◽  
Polar Regions ◽  
Imaging Data ◽  
Patterned Ground ◽  
Large Lakes ◽  
Near Surface ◽  
Crater Lakes ◽  
Recent Climate ◽  
Liquid Flows

Liquid water is generally only meta-stable on Mars today; it quickly freezes, evaporates or boils in the cold, dry, thin atmosphere (surface pressure is about 200 times lower than on Earth). Nevertheless, there is morphological evidence that surface water was extensive in more ancient times, including the Noachian Epoch (∼4.1 Ga to ∼3.7 Ga bp), when large lakes existed and river-like channel networks were incised, and early in the Hesperian Epoch (∼3.7 Ga to ∼2.9 Ga bp), when megafloods carved enormous channels and smaller fluvial networks developed in association with crater-lakes. However, by the Amazonian Epoch (∼3.0 Ga to present), most surface morphogenesis associated with liquid water had ceased, with long periods of water sequestration as ice in the near-surface and polar regions. However, inferences from observations using imaging data with sub-metre pixel sizes indicate that periglacial landscapes, involving morphogenesis associated with ground-ice and/or surface-ice thaw and liquid flows, has been active within the last few million years. In this paper, three such landform assemblages are described: a high-latitude assemblage comprising features interpreted to be sorted clastic stripes, circles and polygons, non-sorted polygonally patterned ground, fluvial gullies, and solifluction lobes; a mid-latitude assemblage comprising gullies, patterned ground, debris-covered glaciers and hillslope stripes; and an equatorial assemblage of linked basins, patterned ground, possible pingos, and channel-and-scarp features interpreted to be retrogressive thaw-slumps. Hypotheses to explain these observations are explored, including recent climate change, and hydrated minerals in the regolith ‘thawing’ to form liquid brines at very low temperatures. The use of terrestrial analogue field sites is also discussed.

scholarly journals Multiple rock-slope failures from Mannen in Romsdal Valley, western Norway, revealed from Quaternary geological mapping and 10Be exposure dating

The Holocene ◽  
2018 ◽  
Vol 28 (12) ◽  
pp. 1841-1854 ◽  
Author(s):  
Paula Hilger ◽  
Reginald L Hermanns ◽  
John C Gosse ◽  
Benjamin Jacobs ◽  
Bernd Etzelmüller ◽  
...  
Keyword(s):  
Slope Failure ◽  
Rock Slope ◽  
Significant Risk ◽  
Geological Mapping ◽  
Slope Instability ◽  
Permafrost Degradation ◽  
Geomorphological Mapping ◽  
Exposure Dating ◽  
Western Norway ◽  
Air Temperatures

Oversteepened valley walls in western Norway have high recurrences of Holocene rock-slope failure activity causing significant risk to communities and infrastructure. Deposits from six to nine catastrophic rock-slope failure (CRSF) events are preserved at the base of the Mannen rock-slope instability in the Romsdal Valley, western Norway. The timing of these CRSF events was determined by terrestrial cosmogenic nuclide dating and relative chronology due to mapping Quaternary deposits. The stratigraphical chronology indicates that three of the CRSF events occurred between 12 and 10 ka, during regional deglaciation. Congruent with previous investigations, these events are attributed to the debuttressing effect experienced by steep slopes following deglaciation, during a period of paraglacial relaxation. The remaining three to six CRSF events cluster at 4.9 ± 0.6 ka (based on 10 cosmogenic 10Be samples from boulders). CRSF events during this later period are ascribed to climatic changes at the end of the Holocene thermal optimum, including increased precipitation rates, high air temperatures and the associated degradation of permafrost in rock-slope faces. Geomorphological mapping and sedimentological analyses further permit the contextualisation of these deposits within the overall sequence of post-glacial fjord-valley infilling. In the light of contemporary climate change, the relationship between CRSF frequency, precipitation, air temperature and permafrost degradation may be of interest to others working or operating in comparable settings.

The enigma of large sorted stone stripes in the tropical Ethiopian Highlands

2020 ◽  
Author(s):  
Alexander Raphael Groos ◽  
Janik Niederhauser ◽  
Naki Akçar ◽  
Heinz Veit
Keyword(s):  
Active Layer ◽  
Late Pleistocene ◽  
Small Scale ◽  
Mean Annual Temperature ◽  
Seasonal Temperature ◽  
Ethiopian Highlands ◽  
Tropical Mountains ◽  
Freeze Thaw ◽  
Exposure Dating ◽  
Ice Cap

&lt;p&gt;The Bale Mountains in the southern Ethiopian Highlands (7-8&amp;#176;N) are formed of multiple superimposed flood basalts and comprise Africa&amp;#8217;s largest plateau above 4000 m. Glacial and periglacial landforms are well-preserved and facilitate the reconstruction of the paleoclimate and landscape of the afro-alpine environment. During the Late Pleistocene, an ice cap covered the central part of the plateau and outlet glaciers extended down into the northern valleys. A striking geomorphological feature on the plateau are large sorted stone stripes that consist of hardly-weathered columnar basalt and are up to 2 m deep, 15 m wide and 200 m long. The stone stripes are located between 3850 and 4050 m at gentle slopes (4-8&amp;#176;) of two volcanic plugs 3-5 km south of the highest peak (Tullu Dimtu, 4377 m) and in the far west of the plateau. Sorted patterned grounds of similar size are characteristic for periglacial environments of the high latitudes, but unique for tropical mountains since their formation requires permafrost and a deep active layer. While diurnal freeze-thaw cycles in tropical mountains are sufficient for the genesis of small-scale patterned grounds, the sorting of large basalt columns (length &gt;2 m, diameter &gt;40 cm) assumes seasonal (or multi-annual) freeze-thaw cycles and a deep active layer. When and under which climatic conditions the sorted stone stripes in the Bale Mountains formed, remains an unsolved mystery. The stone stripes might have developed during the Late Pleistocene under periglacial conditions in close proximity to the ice cap or after deglaciation (~15-14 ka). To assess the timing of the final stagnation of the stone stripes, we determined the age of six basalt columns from two different stripes using &lt;sup&gt;36&lt;/sup&gt;Cl surface exposure dating. In addition, we installed temperature data logger in 2, 10 and 50 cm depth across the plateau and between the stone stripes to investigate the present thermal conditions and diurnal and seasonal temperature variations in the ground. The difference between the measured mean annual temperature and presumed average ground temperature for permafrost (&amp;#8804;0&amp;#176;C) indicates an extreme temperature depression on the plateau of &amp;#8805;10&amp;#176;C during the formation period of the sorted stone stripes. Such a Late Pleistocene cooling would be unprecendented in the tropical mountains. Finally, we applied a simple statistical model forced with meteorological data from a nearby weather station to simulate ground temperatures and test which climatic preconditions are necessary for the formation of sporadic permafrost in the Bale Mountains.&lt;/p&gt;

scholarly journals Freeze-Thaw Tolerance and Clues to the Winter Survival of a Soil Community

2006 ◽  
Vol 72 (3) ◽  
pp. 1784-1792 ◽  
Author(s):  
Virginia K. Walker ◽  
Gerald R. Palmer ◽  
Gerrit Voordouw
Keyword(s):  
Polar Regions ◽  
Pseudomonas Chlororaphis ◽  
Gene Fragment ◽  
Freezing And Thawing ◽  
Soil Community ◽  
Ice Recrystallization ◽  
Freeze Thaw ◽  
Subzero Temperatures ◽  
Single Colony ◽  
16S Rna

ABSTRACT Although efforts have been made to sample microorganisms from polar regions and to investigate a few of the properties that facilitate survival at freezing or subzero temperatures, soil communities that overwinter in areas exposed to alternate freezing and thawing caused by Foehn or Chinook winds have been largely overlooked. We designed and constructed a cryocycler to automatically subject soil cultures to alternating freeze-thaw cycles. After 48 freeze-thaw cycles, control Escherichia coli and Pseudomonas chlororaphis isolates were no longer viable. Mixed cultures derived from soil samples collected from a Chinook zone showed that the population complexity and viability were reduced after 48 cycles. However, when bacteria that were still viable after the freeze-thaw treatments were used to obtain selected cultures, these cultures proved to be >1,000-fold more freeze-thaw tolerant than the original consortium. Single-colony isolates obtained from survivors after an additional 48 freeze-thaw cycles were putatively identified by 16S RNA gene fragment sequencing. Five different genera were recognized, and one of the cultures, Chryseobacterium sp. strain C14, inhibited ice recrystallization, a property characteristic of antifreeze proteins that prevents the growth of large, potentially damaging ice crystals at temperatures close to the melting temperature. This strain was also notable since cell-free medium derived from cultures of it appeared to enhance the multiple freeze-thaw survival of another isolate, Enterococcus sp. strain C8. The results of this study and the development of a cryocycler should allow further investigations into the biochemical and soil community adaptations to the rigors of a Chinook environment.

Micro-relief development in polygonal patterned ground in the Dry Valleys of Antarctica

2011 ◽  
Vol 75 (2) ◽  
pp. 347-355 ◽  
Author(s):  
Bernard Hallet ◽  
Ron Sletten ◽  
Kevin Whilden
Keyword(s):  
Remote Sensing ◽  
Numerical Model ◽  
Ground Surface ◽  
Field Measurements ◽  
Polar Regions ◽  
Dry Valleys ◽  
Patterned Ground ◽  
Viscous Material ◽  
Surface Displacements ◽  
Subsurface Material

AbstractPolygonal patterned ground in polar regions of both Earth and Mars has received considerable attention. In comparison with the size, shape, and arrangement of the polygons, the diverse micro-relief and topography (termed here simply “relief”) of polygonal patterned ground have been understudied. And yet, the relief reflects important conditions and processes occurring directly below the ground surface, and it can be observed readily in the field and through remote sensing. Herein, we describe the relief characteristic of the simplest and relatively young form of patterned ground in the Dry Valleys of Antarctic. We also develop a numerical model to examine the generation of relief due to subsurface material being shouldered aside contraction cracks by incremental sand wedges growth, and to down-slope creep of loose granular material on the surface. We model the longterm subsurface deformation of ice-cemented permafrost as a non-linear viscous material. Our modeling is guided and validated using decades of field measurements of surface displacements of the permafrost and relief. This work has implications for assessing the activity of surfaces on Earth and Mars, and much larger scale potential manifestations of incremental wedging in icy material, namely the distinct paired ridges on Europa.

Timing and Extent of Late Quaternary Glaciation in the Ahuriri River Valley, Southern Alps, New Zealand

2021 ◽  
Author(s):  
Levan Tielidze ◽  
Shaun Eaves ◽  
Kevin Norton ◽  
Andrew Mackintosh
Keyword(s):  
New Zealand ◽  
Large Scale ◽  
Late Quaternary ◽  
Southern Alps ◽  
River Valley ◽  
Entire Study ◽  
Geomorphological Mapping ◽  
Exposure Dating ◽  
Quaternary Glaciation ◽  
Exposure Ages

&lt;p&gt;Some valleys in South Island, New Zealand already have a number of well-dated glacier records. However, understanding of the precise timing of old glacial events in many valleys still remains poor. For this purpose, the cosmogenic &lt;sup&gt;10&lt;/sup&gt;Be surface exposure dating technique was used to constrain the timing and extent of late Quaternary glaciation in the Ahuriri River valley, Southern Alps, New Zealand. The 33 &lt;sup&gt;10&lt;/sup&gt;Be surface-exposure ages from two different moraine complexes range from 16.6&amp;#177;0.4 ka to 19.7&amp;#177;0.5 ka suggesting rapid glacier recession (~17 km) during the last deglaciation.&lt;/p&gt;&lt;p&gt;Field observation and geomorphological mapping were also used to investigate the extent and drivers of glaciation in this valley. For the final step, we created detail and comprehensive map of the glacial geomorphology in an area covered by palaeo Ahuriri Glacier, in the central Southern Alps. Geomorphological mapping from high-resolution aerial imagery, large scale topographical maps, average resolution DEM, and several field investigations allowed us to produce the 1:38,000 scale map for the entire study site covering an area of about 532 km&lt;sup&gt;2&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;This newly created map along with the new &lt;sup&gt;10&lt;/sup&gt;Be surface exposure dataset will help us in better understanding of past glacier-climate interactions in the Southern Alps and in the Southern Hemisphere in general.&lt;/p&gt;

Landscape evolution of the southeastern Tibetan Plateau – Temporal and spatial relationships between glacial and fluvial landforms

2020 ◽  
Author(s):  
Ramona A.A. Schneider ◽  
Arjen P. Stroeven ◽  
Robin Blomdin ◽  
Natacha Gribenski ◽  
Marc W. Caffee ◽  
...  
Keyword(s):  
Landscape Evolution ◽  
Active Regions ◽  
Luminescence Dating ◽  
Spatial Correlations ◽  
Geomorphological Mapping ◽  
Exposure Dating ◽  
Fluvial Terraces ◽  
Infrared Stimulated Luminescence ◽  
Tectonically Active ◽  
Temporal And Spatial

&lt;p&gt;Landscape system components interact in ways which are not yet fully understood, and in tectonically active regions it is of particular interest whether endogenic or exogenic factors are the main drivers of landscape evolution. For example, fluvial terraces may form in response to exogenic disturbances like climatic changes or to endogenic forces like tectonic uplift. This study explores how temporal and spatial correlations between end moraines (denoting the advance of glaciers due to climate change) and fluvial terraces can yield insights about exogenic-endogenic processes determining landscape evolution during the Quaternary on the southern margin of the Shaluli Shan plateau, SE Tibet, a formerly glaciated and tectonically active region. A high-resolution TanDEM-X Digital Elevation Model (12 m) was used to produce detailed geomorphological maps of glacial valleys, marginal moraines, glacial lineations, and fluvial terraces. The geomorphological mapping was complemented with geomorphological and sedimentological field observations. Samples for Optically Stimulated Luminescence dating were taken from extensive and distinct terraces located in pull-apart basins bordering the plateau and samples for cosmogenic nuclide exposure dating were collected from selected boulders on end moraines formed by valley glaciers draining the Mt Genie massif on the Shaluli Shan plateau. Infrared stimulated luminescence (IRSL) signals from feldspar multi grains aliquots, and &lt;sup&gt;10&lt;/sup&gt;Be and &lt;sup&gt;26&lt;/sup&gt;Al concentrations from quartz, were used to determine depositional ages of terraces and moraines, respectively. In combining both dating techniques, we compare the timing of glacial expansions with the depositonal ages of the terraces to tease out the effects of exogenic and endogenic drivers on terrace formation and to formulate a conceptual model of landscape evolution.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document