Geomorphological Traces Research Articles

The Role of Moisture Conveyor Belts for Precipitation in the Atacama Desert

AbstractIn the hyperarid Atacama Desert in northern Chile, rare precipitation events can leave long‐lasting geomorphological traces and have strong impacts on biota. While moisture conveyor belts (MCBs) and atmospheric rivers (ARs) have been associated with extreme precipitation in semiarid regions, their role for the Atacama Desert has not been previously investigated. This study reveals that about four MCBs per year make landfall in the Atacama Desert. According to simulated precipitation, 40–80% of the total precipitation between the coast and the Andean foothills is associated with MCBs. A case study reveals an elevated moisture transport decoupled from the maritime boundary layer, which is generalized by a composite analysis. Back trajectories reveal the Amazon Basin as the main source of moisture. MCB landfall times are derived from the AR catalog by Guan and Waliser (2015), https://doi.org/10.1002/2015jd024257. Implications of the results on paleoclimate reconstructions are discussed.

Meteorite crater re-interpreted as iceberg pit in west-central Sweden

ABSTRACT This study shows the occurrence of numerous iceberg imprints on the bottom of former ice-dammed lakes in Härjedalen, west-central Sweden. Discussion of the genesis of the so-called “impact crater” known as the Tor structure at Torbygget, which is located in this area, motivated an examination of the area using high-resolution digital elevation models. Previous investigations have suggested that this crater was created by a meteorite impact about 2000 years ago, forming a semi-round depression. The results of our investigation clearly indicate that the feature was formed by a grounding iceberg, scouring the bed of an ice-dammed lake during deglaciation about 11 000-10 000 cal. BP. Geomorphic evidence of an ice-dammed lake (multiple and abundant well-developed shorelines) are consistent with earlier mapping efforts in the area. Furthermore, an abundance of geomorphological traces of iceberg activity is found within the paleo-ice-dammed lake basins. Based on this we suggest that the depression at Torbygget is not an impact crater but formed by a grounded iceberg.

Mapping War Geoheritage: Recognising Geomorphological Traces of War

Abstract In the topography of war landscapes the remains of war are found in the form of trenches, bombing craters and remnants of war infrastructure. Today war landscapes are “overlaid” by post-war “layers” of cultural landscapes. It requires non-invasive remote-sensing methods, e.g. time series of aerial photographs and high-resolution terrain models (LiDAR digital terrain model) to recognize these landscapes. In the study area on Kras Plateau (SW Slovenia) over one hundred kilometres of World War I trenches are preserved in the NW part of the plateau (app. 72 km2) in the present-day topography and represent tangible war geoheritage. But much of these geoheritage was also lost in post-war periods, e.g. near the village of Vrtojba (SW Slovenia) where in 1917 over 12 km of World War I trenches existed, but a century later no traces of war are visible in the present-day topography. Almost two hundred World War I bomb craters also existed around the village that are also not existent in the topography any more. Many anthropo-geomorphological traces of war are thus preserved only virtually and present intangible war geoheritage.

Repeated megafloods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000 years

Cataclysmic outburst floods transformed landscapes and caused abrupt climate change during the last deglaciation. Whether such events have also characterized previous deglaciations is not known. Arctic marine cores hint at megafloods prior to Oxygen Isotope Stage (OIS) 2, but the overprint of successive glaciations means that geomorphological traces of ancient floods remain scarce in Eurasia and North America. Here we present the first well-constrained terrestrial megaflood record to be linked with Arctic archives. Based on cosmogenic-nuclide exposure dating and optically stimulated luminescence dating applied to glacial-lake sediments, a 300-m deep bedrock spillway, and giant eddy-bars > 200-m high, we reconstruct a history of cataclysmic outburst floods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000-years. Three megafloods have reflected the rhythm of Eurasian glaciations, leaving traces that stretch more than 3500 km to the Lena Delta. The first flood was coincident with deglaciation from OIS-4 and the largest meltwater spike in Arctic marine-cores within the past 100,000 years (isotope-event 3.31 at 55.5 ka). The second flood marked the lead up to the local Last Glacial Maximum, and the third flood occurred during the last deglaciation. This final 3000 km3 megaflood stands as one of the largest freshwater floods ever documented, with peak discharge of 4.0–6.5 million m3s−1, mean flow depths of 120–150 m, and average flow velocities up to 21 m s−1.

Mangala Valles, Mars: A reassessment of formation processes based on a new geomorphological and stratigraphic analysis of the geological units

Mangala Valles has always been viewed as the typical outflow channel formed by catastrophic floods of water. A new analysis has shown that the geomorphological traces of fluvial or lacustrine processes within Mangala Valles can be better explained by fluid lava flooding the channels and filling pre-existing impact craters. As for the circum-Chryse outflow channels, where no clear source of water or mechanism able to replenish water at its hydraulic head is observed, there is no geologic trace of a sudden removal of a volume of water (ice) necessary to carve Mangala Valles. Neither maars nor rootless cones, typical volcanic features indicative of interaction between lava and ground ice, were found. Past works suggested that the formation of Mangala Valles occurred in late Amazonian age when the climate of Mars was similar to that seen today, that is absolutely not liquid water friendly. The present work shows how the origin of Mangala Valles may go back to Noachian or even Pre-Noachian when other studies have concluded that the climate was not liquid water friendly. Even assuming limited periods of obliquity favourable to liquid water in the history of Mars, which is at odds with the widespread presence of unaltered olivine and jarosite, it is very difficult to find plausible mechanisms of aquifer recharge or signs of catastrophic water release at the Notch of Mangala Valles that could feed the multiple episodes, or even a single episode, of fluvial flooding suggested in the literature. This evidence and other analysis will show that the presence of water and, eventually, ground ice is not incontrovertible in the equatorial regions and should not be given for granted as commonly done so far in the literature. The geomorphological analysis of the Mars Reconnaissance Orbiter (MRO) images provided in this paper, combined with THEMIS and MOLA data, show how Mangala Fossa, from which Mangala Valles originated as a breakout, is an erosional channel formed by the flow of lava in a original tube coming from Daedalia Planum rather than a tectonic graben or the sign of a dike rupturing to the surface.

Geomorphological records of extreme floods and their relationship to decadal-scale climate change

Extreme rainfall and flood events in steep upland catchments leave geomorphological traces of their occurrence in the form of boulder berms, debris cones, and alluvial fans. Constraining the age of these features is critical to understanding (i) landscape evolution in response to past, present, and future climate changes; and (ii) the magnitude–frequency of extreme, ungauged floods in small upland catchments. This research focuses on the Cambrian Mountains of Wales, UK, where lichenometric dating of geomorphological features and palaeohydrological reconstructions is combined with climatological data and documentary flood records. Our new data from Wales highlight a distinct flood-rich period between 1900 and 1960, similar to many other UK lichen-dated records. However, this study sheds new light on the underlying climatic controls on upland flooding in small catchments. Although floods can occur in any season, their timing is best explained by the Summer North Atlantic Oscillation (SNAO) and shifts between negative (wetter than average conditions with regular cyclonic flow and flooding) and positive phases (drier than average conditions with less frequent cyclonic flow and flooding), which vary from individual summers to decadal and multidecadal periods. Recent wet summer weather, flooding, and boulder-berm deposition in the UK (2007–2012) are related to a pronounced negative phase shift of the SNAO. There is also increasing evidence that recent summer weather extremes in the mid-latitudes may be related to Arctic amplification and rapid sea ice loss. If this is the case, continuing and future climate change is likely to mean that (i) unusual weather patterns become more frequent; and (ii) upland UK catchments will experience heightened flood risk and significant geomorphological changes.

Geomorphological traces of conflict in high-resolution elevation models

High-resolution digital elevation models, often derived from airborne lidar, are rapidly gaining importance in both archaeology and geomorphology, in particular where these two disciplines overlap in their interest in anthropogenic changes to the relief of the earth surface (“archaeogeomorphology”). Inter-group and inter-state conflict are one aspect of human behaviour which commonly causes such relief changes. Conflict archaeology and conflict geomorphology, which are both young sub-disciplines within their scientific fields, have until now only touched upon a small part of the wide range of issues which they can encompass. While conflict archaeology has for a long time been almost synonymous with battlefield archaeology, the few papers explicitly discussing conflict geomorphology are mainly concerned with the impact of bombing on soil geomorphology. The application of high-resolution digital elevation models in investigating past conflicts can and should, however, encompass all geomorphological traces of conflict. These include defensive structures such as earthworks, primary and secondary traces of warfare itself (e.g. bomb craters and rubble mountains), conflict-related traces associated with military training and weapons testing facilities as well as, potentially, traces of conflict sustenance (e.g. conflict-related mining and infrastructure). Examples highlight the potential of high-resolution digital elevation models for the detection, mapping and quantification of conflict-related relief changes and thus for the understanding of conflicts. As suitable data are becoming increasingly available, the study of prehistoric and historic conflicts will benefit across the discipline boundaries between archaeology and geomorphology. In the field of heritage management, the detection, visualisation and protection at landscape-scale of what is often seen as “dark” heritage is expected to gain importance.

Geomorphological Traces of the Younger Pleistocene Glaciation in the Central Part of the Velebit Mt.

On the central part of the Velebit Mountain the traces of the Pleistocene glaciation have been found. The domination of the dissected relief, characterized by numerous elevations and depressions, in the conditions of low temperatures and richess of snow precipitation during the Pleistocene were a very good predisposition for glaciation development on the central part of the Velebit Mt.

Sedimentologic and geomorphologic tsunami imprints worldwide—a review

Tsunami events with extreme effects on sedimentary transport or considerable alterations of the coastal configuration are rather rare regarding human history, but considering geological timescales they occur frequently. At least 100 megatsunami in different parts of the world have been recorded in the past 2000 years—but presumably far more have failed to be noticed during historical times and are not mentioned either in written or oral ancient records. Therefore, the topic of paleotsunami requires inevitable sedimentological and geomorphological research. However, field research concerning paleotsunami is astonishingly rare within the scientific approach and only 5% of the existing tsunami literature is related to this subject. Future efforts in paleotsunami research should focus on the geological evidence of these mega-events to clarify their contribution to coastal forming processes. This paper reviews the state-of-the-art knowledge of sedimentologic and geomorphic imprints of tsunami along the world's coastlines in order to highlight the need for more detailed studies of paleotsunami depositional and geomorphological traces.

Global ice volume variations through the last glacial cycle simulated by a 3-D ice-dynamical model

A coupled ice sheet—ice shelf—bedrock model was run at 20 km resolution to simulate the evolution of global ice cover during the last glacial cycle. The mass balance model uses monthly mean temperature and precipitation as input and incorporates the albedo—mass balance feedback. The model is forced by the GRIP and Vostok—derived temperature records (and by sea level and solar radiation variations), which are distributed spatially and seasonally. Model simulations show that at the last glacial maximum (LGM) a volume of ice representing about 65 m of sea level equivalent is stored on the Eurasian continent, whereas North America stores 42 m. The other regions (Greenland, Tibet, South-America and Antarctica) contribute about 17 m to global sea level lowering at the LGM compared to present day. Sensitivity experiments show that the ice volumes of the Eurasian and North American ice sheets are particularly sensitive to summer temperature changes. Finally, the timing and mechanism of grounded ice formation and expansion for the last glacial were studied for the Eurasian and North American continents. Ice sheet formation begins at 118 kyr BP in the Barents and Kara Sea region, over Baffin Island and in the high Cordilleran Range following a 4°C cooling. Alternating regions of ice sheet expansion by direct snowfall, ice flow and grounding of ice shelves can be identified. These relate to specific geomorphological traces, and may as such help in model validation.