Unconsolidated Debris Research Articles

A multi-millennial record of rock glacier ice chemistry (Lazaun, Italy)

Active rock glaciers—known as mixtures of unconsolidated debris with interstitial ice, ice lenses or a core of massive ice—are widespread indicators of mountain permafrost. The age of a frozen rock glacier core in the Central European Alps (Lazaun, Italy) was dated to about 10,000 years. Here we report on the chemical composition of the frozen Lazaun core. The ice containing part of the core extended from about 2.8 m down to 24 m depth and consisted of two lobes—both a mix of ice and debris, separated by more than 3 m thick almost ice-free layer. The two lobes of the core showed layers of high solute content and peak values of electrical conductivity exceeding 1,000 μS/cm, but they differed in acidity and metal concentration. High acidity (minimum pH of 4.15) and high levels of elements like nickel, cobalt, zinc, manganese, iron and aluminum characterized the upper lobe, while neutral to alkaline pH and low metal values prevailed in the bottom lobe. We attributed solutes accumulated in the ice matrix to the weathering of bedrock minerals, with peak values favored by the oxidation of pyrite, or by an enhanced reactive surface area in fine-grained sediment layers. The chemical composition of the ice core also revealed signals of prehistoric atmospheric deposition from different sources including wood combustion, metal ore mining, and large volcanic eruptions (Thera, Aniakchak II). To our knowledge, this is the first study that presents the chemical stratigraphy of an entire rock glacier ice core.

Tracing the Long-Term Evolution of Land Cover in an Alpine Valley 1820–2015 in the Light of Climate, Glacier and Land Use Changes

Alpine glacial environments and their fluvial systems are among those landscapes most comprehensively affected by climate change. Typically, studies on the consequences of climate change in such environments, e.g., glacier retreat, cover a maximum of 70 years, reflecting the availability of orthophotos or satellite images. This study addresses the long-term transformation processes in a glaciated catchment and highlights the role of human agency in a changing Alpine environment. In order to identify land cover changes between 1820 and 2015 in the Long-Term Ecosystem Research (LTER) site “Jamtal” (Tyrol, Austria) we apply a “regressive-iterative GIS reconstruction method” combining both historical maps and optical remote sensing data. Below 2,100 m a.s.l. the Jamtal experienced a massive 62% decline of unvegetated debris areas and bedrock outcrops (so-called “wasteland”) that was mainly transformed to grassland and sparsely wooded areas. Forests increased by an outstanding 323% and grassland was replaced by sparsely or densely wooded areas. This primarily reflects the abandonment of agricultural uses at unfavourable remote sites. In the higher (formerly) glaciated subbasin, ice-covered areas declined by 55%, which was associated with a major (82%) growth of exposed wasteland. Concurrently, Alpine grassland expanded by 196% and krumholz even by 304%. Approximately half of the new fluvial system that evolved in deglaciated areas between 1870 and 1921 still existed in 2015. Unconsolidated debris buried almost one fifth of the new channels, and almost one third was colonized by vegetation. Recent data show that the deglaciation process is much faster than the colonization process by Alpine vegetation. Accordingly, the extent of wasteland has expanded and potentially amplifies the sediment supply to the fluvial system. Alterations in high Alpine hydrological and sediment/debris regimes significantly affect human use in lower, more favourable areas of the Alpine region. The long-term investigation of the Alpine landscape reveals that the transformation processes have accelerated in recent decades.

Pronounced increase in slope instability linked to global warming: A case study from the eastern European Alps

AbstractIn recent decades, slope instability in high‐mountain regions has often been linked to increase in temperature and the associated permafrost degradation and/or the increase in frequency/intensity of rainstorm events. In this context we analyzed the spatiotemporal evolution and potential controlling mechanisms of small‐ to medium‐sized mass movements in a high‐elevation catchment of the Italian Alps (Sulden/Solda basin). We found that slope‐failure events (mostly in the form of rockfalls) have increased since the 2000s, whereas the occurrence of debris flows has increased only since 2010. The current climate‐warming trend registered in the study area apparently increases the elevation of rockfall‐detachment areas by approximately 300 m, mostly controlled by the combined effects of frost‐cracking and permafrost thawing. In contrast, the occurrence of debris flows does not exhibit such an altitudinal shift, as it is primarily driven by extreme precipitation events exceeding the 75th percentile of the intensity‐duration rainfall distribution. Potential debris‐flow events in this environment may additionally be influenced by the accumulation of unconsolidated debris over time, which is then released during extreme rainfall events. Overall, there is evidence that the upper Sulden/Solda basin (above ca. 2500 m above sea level [a.s.l.]), and especially the areas in the proximity of glaciers, have experienced a significant decrease in slope stability since the 2000s, and that an increase in rockfalls and debris flows during spring and summer can be inferred. Our study thus confirms that “forward‐looking” hazard mapping should be undertaken in these increasingly frequented, high‐elevation areas of the Alps, as environmental change has elevated the overall hazard level in these regions.

Airborne Geophysical Imaging of Weak Zones on Iliamna Volcano, Alaska: Implications for Slope Stability

AbstractWater‐saturated, hydrothermally altered rocks reduce the strength of volcanic edifices and increase the potential for sector collapses and far‐traveled mass flows of unconsolidated debris. Iliamna Volcano is an andesitic stratovolcano located on the western side of the Cook Inlet, ∼225 km southwest of Anchorage and is a source of repeated avalanches. The widespread snow and ice cover on Iliamna Volcano make surface alteration difficult to identify. However, intense hydrothermal alteration significantly reduces both the electrical resistivity and magnetization of volcanic rock and can therefore be identified with airborne geophysical measurements. We use airborne electromagnetic and magnetic data to map snow and ice thickness and identify underlying alteration zones at Iliamna Volcano, Alaska. Resistivities were calculated to an average depth of >300 m, and a 3‐D susceptibility model extends from the surface to the base of the volcano, about 3,000 m below the summit. Geophysical models image low resistivity (<30 ohm‐m) and low susceptibilities near the summit of Iliamna and below its older vent complex, with the low susceptibilities indicating alteration up to ∼800 m in thickness. Thin conductors (∼50–100 m thick) on the edifice slopes coincide with recorded locations of repeated debris avalanches over the past ∼60 years and are attributed to saturated zones at high elevation. Three‐dimensional slope stability models based upon the geophysically constrained alteration distribution suggest the edifice of Iliamna is unstable and could lead to collapse scars ∼400 m deep near the current and former vent complexes.

Assessment of permafrost conditions in the highest mountains of the Balkan Peninsula

The proposed research addresses the problem of permafrost occurrence for the first time in the highest mountains of the Balkan Peninsula. The likely/unlikely presence of ice-rich permafrost in 13 rock glaciers in the Rila and Pirin Mountains was investigated using thermal measurements (e.g., ground surface temperature monitoring, measurements of the bottom temperature of snow cover and late summer alpine spring water temperature measurements) and ground penetrating radar surveys. Based on the thermal records, intact rock glaciers appear likely above 2450 m on north-facing slopes, where incoming solar radiation is small and the pronounced shadow effect of the ridges allow an extended duration of snow cover. Thermal results revealed that the coarse blocks influence the near-surface energy exchange fluxes, confirming the significant influence of the cooling effect of high-porosity unconsolidated debris deposits. The intense ground overcooling during the early winter is mainly the result of temperature-driven air convection, whereas in late winter, the low thermal conductivity of the porous boulder mantle below a thick snow cover can cause ground cooling. Furthermore, the reduced insolation below the late-lying snow patches prevents the ground from heating up during the warm season. At most of the sites, the winter equilibrium temperatures are lower than −3 °C and the mean annual ground surface temperatures are negative or close to 0 °C. Ground penetrating radar (GPR) measurements detected permafrost occurrence in three rock glaciers underneath a thick active layer (4–10 m). Forthcoming research on this topic is needed to evaluate more carefully the importance of local conditions for permafrost preservation.

In situ tribometry with real-time imaging for assessing durability and wear mechanisms of easy-to-clean coatings on glass for touchscreen substrates

Touchscreens are now commonplace around the world, and easy-to-clean (ETC) coatings are integral in ensuring an enhanced usability and interactivity with these devices. In the present work, we evaluate the durability and study the wear mechanisms of a fluorine-containing easy-to-clean coating on glass using an in situ tribometer (TribTik). The TribTik is equipped with a microscope lens and camera system that allows one to image, in real time, the contact area between the glass substrate and the abrading counterpart. Through this unique combination, the instantaneous coefficient of friction and the contact area’s status can be monitored and correlated in situ. The in situ monitoring enables one to stop the abrasion cycles at critical stages of the wear process so that the morphology and composition of the wear tracks can be examined in an effort to understand the wear mechanisms of the ETC. We demonstrate that changes in the instantaneous coefficient of friction (COF) are correlated with changes in the in situ images. Critical stages of wear evolution are also identified via optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Raman analyses. The evolution of the ETC wear mechanism, from start to finish, was found to be described by the following sequence: (1) generation of unconsolidated debris, (2) formation of a layered tribofilm, (3) cracking of the tribofilm, and (4) general failure of the ETC and subsequent damage to the underlying glass substrate. Our study shows that, TribTik, a tribometry system with real-time imaging capability, is a powerful tool to characterize the tribological properties of coatings on touchscreens and/or display substrates.

Volume estimation and evaluation of rotational landslides using multi-temporal aerial photographs in Çağlayan dam reservoir area, Turkey

Four landslide scarps in Neogene sedimentary rocks were observed in the Caglayan dam reservoir area. This study aims to (1) estimate the volume of landslide material that slid into the dam reservoir area within 59-year period and (2) evaluate the reactivations with respect to triggering and predisposing factors such as slope gradient, precipitation, fire, and seismic activity. In this context, field survey was combined with innovative use of multi-temporal historical aerial photographs. Various methods of photogrammetry were employed on four sets of stereo aerial photographs (1953, 1970, 1995, 2012) to identify the boundaries of landslides, to generate digital elevation models (DEMs) from which cross-sectional data and slope maps were extracted. Volumes of landslides were estimated based on height differences between successive DEMs. Spatial mismatch and height errors between successive DEMs were minimized by image to image coregistration and height adjustment, respectively. The height adjustment technique was reevaluated and it was suggested to choose 11 sub-areas independent from the size and location. It is also recommended that the accuracy of the landslide boundaries interpreted from aerial photographs should be cross-checked by overlapped cross-sections of successive years to estimate the volume more precisely. A total volume of 121.78 × 104 m3 material collapsed whereas the largest volume moved in the period between 1953 and 1970 which was linked to a seismic event. Unconsolidated debris and weak rock layers are expected to fail in relation to water level fluctuations in the dam lake. The volume of sliding material will contribute to siltation and shorten the operational life of Caglayan dam.

Spatio-temporal evolution of mass wasting after the 2008 Mw 7.9 Wenchuan earthquake revealed by a detailed multi-temporal inventory

Strong earthquakes in mountainous areas can trigger a large number of landslides that generate deposits of loose and unconsolidated debris across the landscape. These deposits can be easily remobilised by rainfalls, with their movement frequently evolving into catastrophic debris flows and avalanches. This has been the fate of many of the 200,000 co-seismic deposits generated by the 2008 Mw 7.9 Wenchuan earthquake in Sichuan, China. Here we present one of the first studies on the post-seismic patterns of landsliding through a detailed multi-temporal inventory that covers a large portion of the epicentral area (462.5 km2). We quantify changes of size-frequency distribution, active volumes and type of movement. We analyse the possible factors controlling landslide activity and we discuss the significance of mapping uncertainties. We observe that the total number of active landslides decreased with time significantly (from 9189 in 2008 to 221 in 2015), and that post-seismic remobilisations soon after the earthquake (2008–2011) occurred stochastically with respect to the size of the co-seismic deposits. Subsequently (2013–2015), landslide rates remained higher in larger deposits than in smaller ones, particularly in proximity to the drainage network, with channelised flows becoming comparatively more frequent than hillslope slides. However, most of the co-seismic debris remained along the hillslopes and are largely stabilised, urging to rethink the way we believe that seismic activity affects the erosion patterns in mountain ranges.

Recognition and paleoclimatic implications of late-Holocene glaciation on Mt Taranaki, North Island, New Zealand

Evidence for the timings of inter-hemispheric climate fluctuations during the Holocene is important, with mountain glacier moraine systems routinely used as a proxy for climate. In New Zealand such evidence for glacier expansion during the late Holocene is fragmentary and is limited to glaciers in a narrow zone within the Southern Alps. Here, we present the first evidence for late-Holocene glacier expansion on the North Island of New Zealand in the form of two unconsolidated debris ridges on the south side of the stratovolcano, Mt Taranaki/Mt Egmont, at ~1920 m a.s.l. The two ridges are aligned north–south along the western and eastern sides of a small basin (Rangitoto Flat), which is formed between the main Taranaki cone (to the north), and the parasitic cone of Fanthams Peak (to the south). The approximate age of the ridges is constrained by dated eruptive events and the relationship between ridge locations and the spatial positioning of adjacent volcanic landforms. We propose the ridges formed as two lateral moraines on the margins of a cirque glacier during the final construction phase of Fanthams Peak between 3.3 and 0.5 ka BP, during late-Holocene time. This time interval accords with published cosmogenic 10Be dating of moraine-building episodes in the Southern Alps, indicating the Mt Taranaki moraines are a response to the same regional climatic forcings.

Growth and mass wasting of volcanic centers in the northern South Sandwich arc, South Atlantic, revealed by new multibeam mapping

New multibeam (swath) bathymetric sonar data acquired using an EM120 system on the RRS James Clark Ross, supplemented by sub-bottom profiling, reveals the underwater morphology of a ∼ 12,000 km 2 area in the northern part of the mainly submarine South Sandwich volcanic arc. The new data extend between 55° 45′S and 57° 20′S and include Protector Shoal and the areas around Zavodovski, Visokoi and the Candlemas islands groups. Each of these areas is a discrete volcanic center. The entirely submarine Protector Shoal area, close to the northern limit of the arc, forms a 55 km long east–west-trending seamount chain that is at least partly of silicic composition. The seamounts are comparable to small subaerial stratovolcanoes in size, with volumes up to 83 km 3, indicating that they are the product of multiple eruptions over extended periods. Zavodovski, Visokoi and the Candlemas island group are the summits of three 3–3.5 km high volcanic edifices. The bathymetric data show evidence for relationships between constructional volcanic features, including migrating volcanic centers, structurally controlled constructional ridges, satellite lava flows and domes, and mass wasting of the edifices. Mass wasting takes place mainly by strong erosion at sea level, and dispersal of this material along chutes, probably as turbidity currents and other mass flows that deposit in extensive sediment wave fields. Large scale mass wasting structures include movement of unconsolidated debris in slides, slumps and debris avalanches. Volcanism is migrating westward relative to the underlying plate and major volcanoes are asymmetrical, being steep with abundant recent volcanism on their western flanks, and gently sloping with extinct, eroded volcanic sequences to their east. This is consistent with the calculated rate of subduction erosion of the fore-arc.

Geomorphology of snow avalanche impact landforms in the southern Canadian Cordillera

Snow avalanche impact landforms (SAILs) are typically elliptical‐shaped depressions bounded by an arcuate ridge located at the base of avalanche paths. The geomorphology of these features is controlled by the topography of the avalanche path, the availability of unconsolidated debris in the impact area and the ability of the avalanche impacts to displace the available debris in the direction of avalanche flow. Ground‐based snow avalanches move debris by bulldozing, and airborne snow avalanches move sediment by excavation on impact.This paper reports on the geomorphology, and surface age and stability of three SAILs in the southern Canadian Cordillera. Dendrochronology and lichenometry were used to date geomorphic activity at the sites. Evidence of present SAIL stability suggests they result from episodic, high‐magnitude avalanche impact events over many hundreds of years. All three landforms share common morphologies: a water‐filled bowl‐shaped depression distally bounded by an arcuate ridge‐oriented transverse to the avalanche path. Despite sharing many attributes, field investigations revealed that the origin of each SAIL was a function of the local variations in snow avalanche path topography and availability of unconsolidated debris in the impact area. The snow avalanche path associated with the Blackhorn site has a gentle gradient, which suggests that this SAIL is a result of ground‐based avalanches. The SAIL at Spoon Lake appears to be a consequence of a resistant geologic feature that focuses snow avalanches in the impact area and results in explosive excavation. The morphology of the snow avalanche track at Peyto Lake causes large snow avalanches to become airborne prior to impacting and excavating an impact pool. All three SAILs examined in this paper are historically persistent landforms and these observations support previous findings indicating that SAILs require hundreds of years to develop.

Pacific Basin tsunami hazards associated with mass flows in the Aleutian arc of Alaska

We analyze mass-flow tsunami generation for selected areas within the Aleutian arc of Alaska using results from numerical simulation of hypothetical but plausible mass-flow sources such as submarine landslides and volcanic debris avalanches. The Aleutian arc consists of a chain of volcanic mountains, volcanic islands, and submarine canyons, surrounded by a low-relief continental shelf above about 1000–2000 m water depth. Parts of the arc are fragmented into a series of fault-bounded blocks, tens to hundreds of kilometers in length, and separated from one another by distinctive fault-controlled canyons that are roughly normal to the arc axis. The canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes. The volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large-scale sector collapse into the sea. Large scale mass-flow deposits have not been mapped on the seafloor south of the Aleutian Islands, in part because most of the area has never been examined at the resolution required to identify such features, and in part because of the complex nature of erosional and depositional processes. Extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the Aleutian Islands. Because the Aleutian arc is surrounded by deep, open ocean, mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources. To test this hypothesis we present a series of numerical simulations of submarine mass-flow initiated tsunamis from eight different source areas. We consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope. The flows have lengths that range from 40 to 80 km, maximum thicknesses of 400–800 m, and maximum widths of 10–40 km. We also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse, at four locations (Makushin, Cleveland, Seguam and Yunaska SW volcanoes), which represent large to moderate sized events in this region. We calculate tsunami sources using the numerical model TOPICS and simulate wave propagation across the Pacific using a spherical Boussinesq model, which is a modified version of the public domain code FUNWAVE. Our numerical simulations indicate that geologically plausible mass flows originating in the North Pacific near the Aleutian Islands can indeed generate large local tsunamis as well as large transoceanic tsunamis. These waves may be several meters in elevation at distal locations, such as Japan, Hawaii, and along the North and South American coastlines where they would constitute significant hazards.

Holocene landslides in KwaZulu-Natal, South Africa

Research Article| March 01, 2008 Holocene landslides in KwaZulu-Natal, South Africa R.G. Singh; R.G. Singh Council for Geoscience, P.O. Box 900, Pietermaritzburg, 3200, e-mail: rgrow@geoscience.org.za; gabotha@geoscience.org.za Search for other works by this author on: GSW Google Scholar G.A. Botha; G.A. Botha Council for Geoscience, P.O. Box 900, Pietermaritzburg, 3200, e-mail: rgrow@geoscience.org.za; gabotha@geoscience.org.za Search for other works by this author on: GSW Google Scholar N.P. Richards; N.P. Richards School of Geological Sciences, University of KwaZulu-Natal, P/Bag X54001, Durban, 4000, e-mail: Richards@ukzn.ac.za Search for other works by this author on: GSW Google Scholar T.S. McCarthy T.S. McCarthy School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg, 2050, e-mail: mccarthyt@geosciences.wits.ac.za Search for other works by this author on: GSW Google Scholar Author and Article Information R.G. Singh Council for Geoscience, P.O. Box 900, Pietermaritzburg, 3200, e-mail: rgrow@geoscience.org.za; gabotha@geoscience.org.za G.A. Botha Council for Geoscience, P.O. Box 900, Pietermaritzburg, 3200, e-mail: rgrow@geoscience.org.za; gabotha@geoscience.org.za N.P. Richards School of Geological Sciences, University of KwaZulu-Natal, P/Bag X54001, Durban, 4000, e-mail: Richards@ukzn.ac.za T.S. McCarthy School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg, 2050, e-mail: mccarthyt@geosciences.wits.ac.za Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2008, The Clay Minerals Society South African Journal of Geology (2008) 111 (1): 39–52. https://doi.org/10.2113/gssajg.111.1.39 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R.G. Singh, G.A. Botha, N.P. Richards, T.S. McCarthy; Holocene landslides in KwaZulu-Natal, South Africa. South African Journal of Geology 2008;; 111 (1): 39–52. doi: https://doi.org/10.2113/gssajg.111.1.39 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The devastating impact of landslides and secondary instability associated with their unconsolidated debris deposits due to weathering, settlement and groundwater seepage are significant geological threats. Mass movements can impact negatively on urbanisation and represent a critical factor determining landuse zonation during town and regional planning.Mapping and classification of mass movement deposits in the KwaZulu-Natal Province highlighted the more widespread extent of these Quaternary geomorphic disequilibrium indicators than is commonly appreciated. Many of the largest occurrences mapped are palaeo-landslides located in areas of high relief and steep slopes in the Ukhahlamba-Drakensberg footslopes and the major river valleys. Some of these events temporarily blocked river channels resulting in changed channel and floodplain morphology. However, the majority of the landslides identified are smaller, more recent, localized occurrences associated with high intensity rainfall events. Accelerator Mass Spectrometry (AMS) or radiocarbon dating of bulk organic material derived from ponds on back-tilted surfaces (sag ponds) of the palaeo-landslides has yielded minimum ages for the landslide events. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Paraglacial landform assemblages in the Hindukush and Karakoram Mountains

The paper focuses on the evolution of debris landforms in subtropical high-mountain areas. The Karakoram and Hindukush Mountains are characterized by their high volume and variety of debris accumulations. The valley flanks are coated by unconsolidated debris slopes up to 1000 m in height. The valley floors are occupied by expansive debris-flow cones and alluvial fans with escarpment heights of over 100 m. The field investigations in over twenty valleys showed that the major part of those landforms is governed by the late and post-glacial glaciation history. A key role in this glacially-controlled landscape system is played by the slope moraines, which cover the valley flanks up to several hundred meters above the valley floor. The secondary debris supply by resedimentation processes of moraine material and glacially-induced rock failures exceed by far the primary debris production due to weathering processes. Landforms which have been formerly classified as “periglacial talus cones” rather can be considered as glacial or glacially-controlled-landforms. The identified paraglacial landforms can serve as useful palaeoclimatic indicators for the ice-age reconstruction.

How one man warmed to a career in geoscience

Profile by Andrew McBarnet of Prof John Reynolds, an acknowledged world authority on glacial hazard assessment and mitigation (see Special Topic p. 61), but also a vocal advocate of the value of geoscience with a remarkable career to prove it. If you’re searching for an example of how to make geoscience relevant to today’s generation of maths and science shy students, look no further than Prof John Reynolds. His career has been devoted to geoscience across a broad range of activities, but is now increasingly focused on affecting positive change for communities around the world through the application of environmental geoscience. In addition, he is a passionate advocate for his profession, as a public speaker, an educator, and indeed as author of the standard textbook on applied and environmental geophysics for university students. From his small consultancy base in Mold, North Wales he has sought the ear of governments and international agencies in an effort to alert them to the potentially catastrophic dangers posed by natural phenomena such as glacial hazards and earthquakes. For example, glacial lakes in the Himalayas in countries such as Nepal, Bhutan, India, Pakistan, China, Tibet, and Kyrgyzstan are expanding rapidly as a result of global warming. Some of the lakes are inherently unstable, because their dams can be ice cored and consist of unconsolidated rock debris. Just what can happen was shown in 1954 in Tibet when an uncontrolled rise in the water level led to the collapse of a dam which poured an estimated 300,000 m3 of rock and water without warning in a 40 m high flood surge into China. This so called glacial lake outburst flood (GLOF) travelled over 120 km destroying the town of Gyanze and killing thousand of people. Reynolds points out that since the 1950s temperatures have risen significantly so that so that glaciers are retreating at an average of 20-50 m per year. (The science of glacial hazard assessment is discussed in Reynolds’ article in this issue on p. 61)

Numerical simulation of tsunami generation by cold volcanic mass flows at Augustine Volcano, Alaska

Abstract. Many of the world's active volcanoes are situated on or near coastlines. During eruptions, diverse geophysical mass flows, including pyroclastic flows, debris avalanches, and lahars, can deliver large volumes of unconsolidated debris to the ocean in a short period of time and thereby generate tsunamis. Deposits of both hot and cold volcanic mass flows produced by eruptions of Aleutian arc volcanoes are exposed at many locations along the coastlines of the Bering Sea, North Pacific Ocean, and Cook Inlet, indicating that the flows entered the sea and in some cases may have initiated tsunamis. We evaluate the process of tsunami generation by cold granular subaerial volcanic mass flows using examples from Augustine Volcano in southern Cook Inlet. Augustine Volcano is the most historically active volcano in the Cook Inlet region, and future eruptions, should they lead to debris-avalanche formation and tsunami generation, could be hazardous to some coastal areas. Geological investigations at Augustine Volcano suggest that as many as 12–14 debris avalanches have reached the sea in the last 2000 years, and a debris avalanche emplaced during an A.D. 1883 eruption may have initiated a tsunami that was observed about 80 km east of the volcano at the village of English Bay (Nanwalek) on the coast of the southern Kenai Peninsula. Numerical simulation of mass-flow motion, tsunami generation, propagation, and inundation for Augustine Volcano indicate only modest wave generation by volcanic mass flows and localized wave effects. However, for east-directed mass flows entering Cook Inlet, tsunamis are capable of reaching the more populated coastlines of the southwestern Kenai Peninsula, where maximum water amplitudes of several meters are possible.

Ice friction, wear features and their dependence on sliding velocity and temperature

AbstractFriction processes for ice samples sliding on steel have been determined by examining wear and debris morphology with low-temperature scanning electron microscopy and relating the processes to the velocity and temperature of formation. Friction experiments were carried out over a temperature range of −27 to −0.5°C and velocity range of 0.008–0.37 m s−1. Data were used to develop a friction map. Low friction (µ < 0.1) at high temperature (–3.4ºC)–low velocity (0.02 ms−1), and low temperature (–25.1ºC)–high velocity (0.30 ms−1) is due to the presence of liquid water which lubricates the sliding interface. Diagnostic morphologies for lubricated sliding include the presence of residual liquid in wear grooves and the development of a consolidated mass of debris on the trailing side of the wear surface with distinct grain boundaries and spheroidal air bubbles. High friction (µ > 0.15) at low temperature (−24.5ºC)–low velocity (0.03 m s−1) results from insufficient lubrication at the sliding interface, leading to plastic deformation. Diagnostic morphologies of plastic deformation include scuffing features on the wear surface and the accumulation of sheets of unconsolidated debris on the trailing edge of the wear surface.

The thickness and internal structure of Fireweed rock glacier, Alaska, U.S.A., as determined by geophysical methods

AbstractGeophysical investigations on rock glaciers are often difficult because rock glaciers are covered by an unconsolidated debris mantle a few meters thick, are typically <50 m thick and are composed of an ice—rock mixture of unknown composition. Transient electromagnetics (TEM) is a method that allows some of these difficulties to be minimized, and data collection is relatively efficient. TEM, with calibration from terminus exposure, was used to determine the thickness (~60 m) of Fireweed rock glacier, Alaska, U.S.A., under complex valley geometry. A conductive layer beneath the rock glacier was identified, and its distribution is consistent with a till-like layer. Seismic refraction, used to resolve the debris-mantle thickness (2–4 m), suggests the presence of a discontinuity at 18–28 m depth within the rock glacier. The discontinuity is also indicated in the radio-echo sounding and the TEM data, but to a lesser extent. This discontinuity is important because the motion of the rock glacier may occur across this as a “shear plane”.

Comparison of deep-water coral reefs and lithoherms off southeastern USA

Two types of deep-water coral bioherms occur off the coast of southeastern United States: Oculina and Lophelia/Enallopsammia. The deep-water Oculina bioherms form an extensive reef system at depths of 70–100 m along the shelf edge off central eastern Florida. These reefs are comprised of numerous pinnacles and ridges, 3–35 m in height. Each pinnacle is a bank of unconsolidated sediment and coral debris that is capped on the slopes and crest with living and dead colonies of Oculina varicosa, the ivory tree coral. In comparison, deep-water reefs of Lophelia pertusa and Enallopsammia profunda corals occur at depths of 500–850 m (maximum 150-m relief) along the base of the Florida-Hatteras slope in the Straits of Florida. On the western edge of the Blake Plateau off South Carolina and Georgia, 54-m high banks of Enallopsammia and Lophelia occur at depths of 490–550 m, whereas on the eastern edge of the plateau the reefs form structures 146 m in height and at depths of 640–869 m. The geomorphology and functional structure of both the Oculina and Lophelia reefs are similar. North of Little Bahama Bank, at depths of 1000–1300 m, a region of bioherms is dominated by the coral Solenosmilia sp.; Lophelia is reportedly absent. This paper summarizes 25 years of submersible studies on the deep-water Oculina reefs, describes submersible reconnaissance of deep-water Lophelia reefs off the southeastern United States, and contrasts these types of bioherms with the deep-water lithoherms in the Straits of Florida west of the Bahamas.

Characterization of marine aggregates off Waikiki, O'ahu, Hawai'i

Researchers at the University of Hawai'i at Manoa have been working for the past several years to develop the necessary techniques for finding and quantitatively characterizing offshore unconsolidated carbonate deposits with potential for beach nourishment and use in construction aggregates for tropical island communities. This article examines particular results of this research, with special attention given to the area offshore from Waikiki Beach. Acoustic surveying, water‐jet probing to measure the thickness of unconsolidated material and three different sampling methods were used in this study. Two separate seismic systems were used for the subbottom profiling survey, a Datasonics Bubble‐Pulser® system and a broad‐band, frequency‐modulated ("chirp") prototype system. The following conclusions were reached. (1) Many different types of sediment underlie tropical island carbonate sand deposits and serve as refusing horizons to jet probing. Examples include consolidated or unconsolidated reef debris, beach rock, cemented sand, and various types of conglomerates formed from rhodoliths (coralline algae) or reef detritus. (2) Massive coral growth over clastic deposits is not a common offshore feature in this area, though it does occur in some areas off the Reef Runway. (3) Matrices of the coral Porites compressa, in‐filled with sand, may have acoustic properties similar to those of the sand bodies. Such deposits may be difficult to distinguish from unconsolidated deposits from seismic records alone. (4) Significant new prospects for offshore aggregates were found in the insular shelf offshore from Southern O'ahu. A total of 5,100,000 m3 were mapped off Waikiki. The Makua Shelf deposits in this area presently appear to be the best prospects for commercial development.