Obituaries

Abstract

A rich variety of processes have modified the glacial landscape of the Scottish Highlands since the last glaciers disappeared 11,500 years ago. Many of these processes can be described as paraglacial (glacially-conditioned): retreat of glacier ice has resulted in exposure of metastable sediment sources (rock slopes, drift-mantled slopes and valley-floor glacigenic deposits) that have been reworked over a range of timescales. Much of the reworked sediment has been deposited in paraglacial sediment stores (talus accumulations, debris cones, alluvial fans, valley fills, river terraces and deltas). The trajectory of paraglacial sediment transfer can be approximated by an exhaustion model. A corollary of this model is that all sediment stores eventually undergo a change from net accumulation to net erosion, reflecting the non-renewable nature of sediment sources. This concept helps to explain why most talus accumulations, debris cones and alluvial fans in the Highlands are now relict, and why many floodplains appear to have experienced an initial period of aggradation followed by later river incision and terrace development. Since deglaciation, rock slopes have experienced paraglacial stress release due to differential deglacial unloading. Many rock slopes have remained stable or experienced gradual adjustment through intermittent rockfall. At over 600 sites, however, large-scale rock-slope failure has occurred, either in the form of catastrophic failure with complete or arrested debris runout, or as major slope deformations. Modification of drift-mantled slopes has been dominated by rainstorm-generated debris flows activity, which have stripped sediment from slopes and redeposited it in debris cones. Radiocarbon dating of buried organic horizons shows that debris flows have occurred intermittently throughout the Holocene. Snow avalanches have played only a localized role in paraglacial sediment transfer. The Holocene alluvial history of the Highlands is poorly understood. Some alluvial fans formed during a few exceptional flood events, and there is evidence that postglacial floodplain aggradation peaked in the late Holocene and was succeeded by floodplain incision and terrace development, possibly reflecting upstream reduction in paraglacial sediment supply. Other processes have operated independently of glacial conditioning. The effects of wind action are dominant in the coastal zone, forming dunefields through aeolian reworking of beach sand, and on plateaux in the form of deflation surfaces and sand sheets. Extensive erosion of plateau-top sands and aeolisols occurred in the period AD 1550–1700, a period of exceptional storminess. Small-scale periglacial processes have also been active on high ground throughout the Holocene, including granular weathering of exposed rock surfaces, the development of small-scale frost-sorted patterned ground on unvegetated terrain, and slow downslope movement of solifluction sheets, solifluction lobes and ploughing boulders.     

Catastrophic Rock-Slope Failures in NW Scotland: Quantitative Analysis and Implications

126 postglacial catastrophic rock-slope failures (PRSFs) and 66 debris-free failure scarps (DFFSs) were identified using Google Earth? imagery on Lewisian Gneiss (LG), Torridon Sandstone (TS), Cambrian Quartzite (CQ) and Moine Schist (MS) terrains in NW Scotland. Normalisation of these data for area and gradient shows that RSF density on slopes ≥25° decreases in the sequence MS?>?LG?≈?CQ?>?TS. Most are apparently discordant with structure, suggesting that failure along slope-(sub)parallel joints was more common than failure along bedding or foliation planes. DFFSs represent failure scars from which runout debris has been removed by later glaciation. Eighteen were recorded outside the limits of the Loch Lomond Readvance, implying that they survived the last ice-sheet glaciation, and support the view that many steep upper rock slopes have been dominated by gravity-driven rock detachment rather than glacial erosion. We argue that many RSFs were probably triggered by Lateglacial earthquakes due to fault (re)activation by crustal rebound, as 74% of recorded PRSFs and DFFSs are located at or near slope crests. 44% of recorded PRSFs and DFFSs occur in cirques, suggesting that cirque enlargement during successive glacial-interglacial cycles involved deepening by glacial erosion, headwall retreat by rock-slope failure and removal of RSF debris during subsequent glaciation.     

A Peaty-debris Flow in Glen Docherty,Wester Ross

Glen Docherty has a long history of debris flow activity along the glen’s north east slope, but in early August 2015 a peaty-debris flow was triggered on the glen’s south west slope, involving an initial slide volume of 190?m³ debris/peat, of which 89?m³ consisted of peat. The flow merited study due to (a) its unusual location relative to debris flow activity affecting the rest of the glen, (b) the volume of peat involved and its effect on flow behaviour, (c) the role of immediate post-debris flow fluvial activity and (d) later responses to the event including subsequent weathering, fluvial activity and the potential for debris flow reactivation.     

THE TRAVERSETTE (ITALIA) ROCKFALL: GEOMORPHOLOGICAL INDICATOR OF THE HANNIBALIC INVASION ROUTE*

Numerous small, low volume rockfalls around the crest of the Italian and French Alps, principally formed from calcareous mica schist and metabasalt, have impeded travel across the major cols for millennia. As documented by Polybius and Livy in the ancient literature, Hannibal's Army was blocked by a two-tier rockfall on the lee side of the Alps, a rubble sheet of considerable volume that delayed his exit into the upper Po River Country. An in-depth study of the possible cols reveals that the only such two-tier landform lies below the Col de la Traversette, at ∼2600 m above sea level. In addition, it represents a problem in applied geomorphology, namely, to accurately determine the nature of the surface rubble sheet in Hannibal's time (218 bc ). A reconstruction of the initial deposit, likely Late Glacial, following the retreat of the Po Glacier, is based upon an analysis of the source rock and geological setting. Further specifications on the geometry of the Neoglacial cover sediment are based on weathering characteristics, lichen cover and soil development. The 'myth' that Hannibal fired the rockfall to comminute boulders is plausible given the vegetation records which support tree growth nearby, but is unsubstantiated by the lack of any carbonized rock.     

Some Thoughts on the Origin,Development and Retreat of Slopes

A senior Moscow University geomorphologist suggests that the limited Russian literature on slope development interprets “slope processes” too narrowly, restricting the term largely to mass wasting. Moreover, the convex-concave slope profile is viewed as the mature type under all climatic conditions. Such an approach tends to ignore the common phenomenon of slope retreat, which is presented as a more significant factor in slope development than the processes taking place on the slope itself. Several examples of slope retreat over long distances are given, suggesting that the profiles of retreating slopes depart from the convex-concave model. The author also takes issue with the view that stepped slope profiles tend to be smoothed by mass wasting. In his view, stepped profiles may in fact be further accentuated in slope development, for example, on valley sides made up of alternating soft and hard rock layers and in the case of so-called antiplanation terraces in high-latitude mountains. The author also takes issue with the view that “cattle tracks” are primary slope forms. He suggests they are secondary formations superimposed on ridges and other microrelief forms produced by mass wasting on the slope.     

Scottish landform examples 45: Sgriob na Caillich: a landslide-sourced medial moraine on the Isle of Jura

ABSTRACT

Medial moraines deposited by former glaciers and ice sheets are rare in Scotland. The most prominent example is the Sgriob na Caillich moraine, which consists of two to four parallel belts of angular quartzite boulders that extend northwestwards for over 3.5?km from the SW flank of Beinn an Oir on the Isle of Jura. The boulder belts extend to within 300?m of the present coastline, where they are truncated by a low bluff and raised marine terrace. The source of the moraine coincides with bedrock gullies and cliffs that represent the scars of former rock-slope failure(s), indicating that the moraine debris was sourced by one or more rockfalls or rockslides onto the ice surface after Beinn an Oir had emerged from the thinning ice cover as a nunatak. Exposure dating of boulders on the moraine indicate that it formed at 16.6?±?0.8?ka, consistent with the timing of ice-sheet retreat in this sector. The alignment of the moraine indicates ice-margin retreat to the SE; as regional ice-sheet retreat across the adjacent offshore shelf was to the NE, this anomaly implies that a residual icefield became stranded on Jura during ice-sheet retreat.     

The coastal landslides of Shetland

Little is known of hard-rock coastal landsliding in Scotland. We identify 128 individual coastal landslides or landslide complexes >50 m wide along the coasts of Shetland. Most are apparently translational slides characterized by headscarps, displaced blocks and/or debris runout, but 13 deep-seated failures with tension cracks up to 200 m inland from cliff crests were also identified. Thirty-one sites exhibit evidence of at least localized recent activity. Landslide distribution is primarily determined by the distribution of coastal cliffs >30 m high, and they are preferentially developed on metasedimentary rocks. Analysis of 16 landslides on Fetlar (NE Shetland) indicates that most are translational dip-slip failures; 3 represent deep-seated failures and several exhibit active frontal erosion attributable to basal sapping by storm waves. As these landslides terminate in shallow water, failure was probably initiated when rising sea level resulted in footslope erosion and upslope propagation of instability, causing downslope displacement of landslide blocks on upper slopes. ¹⁰Be exposure dating of two headscarps yielded ages of 4.8?±?0.2 ka and 4.4?±?0.2 ka, consistent with the onset of footslope erosion as sea level rose. Our results suggest that landslides have played a hitherto undocumented but important role in retreat of cliffed coastlines in Scotland.     

The Effect of Shelter on the Temperature and Moisture of Desert Sands

Mechanical shelters, including both covering sand binders and standing windbreaks, are found to be significant not only in reducing wind speed in the surface layer and thus lessening sand drifting, but also in reducing sand temperatures and preserving moisture for optimal plant growth. Shelters are shown to reduce sand temperatures in the midday hours (at a depth of 0.15 m) by 1.5–2.5°C on slopes of southern exposure and by as much as 5.5° on north-facing slopes of sand dunes. The difference in sand-surface temperatures on the windward and lee sides of barriers is found to reach 5° on south-facing slopes and 10° on north-facing slopes. Both covering sand binders and standing windbreaks also tend to reduce evaporation from the sand surface. Stabilized sand dunes are shown to retain 60 percent more moisture on the average than unprotected dunes. Contrary to some statements in the literature, standing windbreaks are found not to produce desiccation of the sand. The reduction of the sand temperature on the shady side of barriers combined with the increase in sand moisture suggest optimal places for plant growth: These are the lee side on south-facing slopes and the windward side on north-facing slopes of sand dunes.     

Field Measurements and Numerical Simulation of Debris Flows from Dolomite Slopes Destabilized during the 2005 Kashmir Earthquake,Pakistan

A devastating earthquake occurred in Kashmir, Pakistan on October 8, 2005. This earthquake resulted from reactivation of a known active fault later defined as the Balakot–Bagh fault, which caused widespread slope failure throughout its stretch, particularly around Muzaffarabad, the provincial capital of Azad Jammu and Kashmir. This slope failure resulted in a huge amount of debris material which flows in deeply incised creeks during monsoon and hits the inhabitants along the valley in Muzaffarabad. Two GPS measurements are carried out along with channel morphometric parameters and observed changes to investigate the effect of debris flows along these creeks during monsoon. Other than the physical measurements, actual debris flow is simulated using the Depth Average Material Point Method (DAMPM) after carrying out parametric study and calibrating the model for subject topographical and geological settings. The generalized effect of different input parameters of the model on debris flow runout features is studied and discussed in detail. After ensuring validation of the numerical tool, the contribution of a single closed-type check dam to decrease runout intensity to its downstream reach is also investigated for different locations to obtain optimized selection.     

Chronology and palaeoenvironment of levantine prehistoric sites as seen from sediment studies

Analysis of sediments from the sites of et-Tabun, Jebel Qafza, and Sefunim in Israel, of Ksar 'Aqil in Lebanon, and of Yabrud Rockshelter I and Jerf 'Ajla in Syria leads to a reconstruction of the environments of deposition, periods of weathering and erosion, and relations to changing sea level during the times of occupation of these sites by prehistoric man. The overlapping sequences span the interval from part or all of the last interglaciation through the time of the last glaciation into historic time. Aeolians and from the last interglacial littoral zone and aeolian silt from more distant deserts dominate the site sediments until the early part of the last glaciation (especially at Tabun), whereas colluvial slope deposits, alluvium (Ksar 'Aqil), and angular rockfall debris are characteristic of the mid-last glaciation sediments in most sites, commonly with an admixture of reworked terra rossa soil sediment. These latter sediments seem to reflect a period or periods of greater available moisture or surface run-off. Prominent unconformities mark many sites at times coincident with the final middle palaeolithic (mousterian) occupations or in the interval between middle palaeolithic and upper palaeolithic occupations. It is not clear, in the absence of firm radiometric dates, whether these hiatuses should be correlated from site-to-site or whether they are site-specific. Freeze/thaw phenomena appear not to have played a significant role, if any at all, in the origin of sediments in coastal Levantine sites, although the middle palaeolithic of the Syrian Desert (Yabrud, Jerf 'Ajla) is contained in typical cryoclastic rubble. Finally, the reconstructed sedimentary environments are compared with the still-too-sparse palynological record for the Near East. Parallels of more humid and less humid climatic intervals throughout the past 60,000 to 70,000 years in both of these records reinforce the growing impression of a regionally fluctuating climate in the eastern Mediterranean region during the time of the last glaciation.     

Evolution of deformation and fault‐related fluid flow within an ancient methane seep system (Eocene,Varna, Bulgaria)

Faults are often important in fuelling methane seep systems; however, little is known on how different components in fault zones control subsurface fluid circulation paths and how they evolve through time. This study provides insight into fault‐related fluid flow systems that operated in the shallow subsurface of an ancient methane seep system. The Pobiti Kamani area (NE Bulgaria) encloses a well‐exposed, fault‐related seep system in unconsolidated Lower Eocene sandy deposits of the Dikilitash Formation. The Beloslav quarry and Beloslav N faults displace the Dikilitash Formation and are typified by broad, up to 80 m wide, preferentially lithified hanging wall damage zones, crosscut by deformation bands and deformation band zones, smaller slip planes and fault‐related joints. The formation of a shallow plumbing system and chimney‐like concretions in the Dikilitash Formation was followed by at least two phases of fault‐related methane fluid migration. Widespread fluid circulation through the Dikilitash sands caused massive cementation of the entire damage zones in the fault hanging walls. During this phase, paths of ascending methane fluids were locally obstructed by decimetre‐thick, continuous deformation band zones that developed in the partly lithified sands upon the onset of deformation. Once the entire damage zone was pervasively cemented, deformation proceeded through the formation of slip planes and joints. This created a new network of more localized conduits in close vicinity to the main fault plane and around through‐going slip planes. ¹³C‐depleted crustiform calcite cements in several joints record the last phase of focused methane fluid ascent. Their formation predated Neogene uplift and later meteoric water infiltration along the joint network. This illustrates how fault‐related fluid pathways evolved, over time, from ‘plumes’ in unconsolidated sediments above damage zones, leading to chimney fields, over widespread fluid paths, deflected by early deformation structures, to localized paths along fracture networks near the main fault.     

The economic development of West Africa

Almost all documented landslides in Scotland belong to one of four categories: non‐rotational rock slope failures (major rockfalls, translational slides, topples or sags, often in some combination); rotational rock slope failures; debris flows; and translational slides in drift or regolith. Non‐rotational rock slope failures are particularly common on Highland metamorphic rocks, especially schists, and on igneous scarps in the Hebrides and Midland Valley; rotational rock slope failures almost invariably occur in weak sedimentary rocks overlain by resistant igneous rocks; and debris flows are most common on sandy drift or regolith. Former glacial activity has also been of importance in determining landslide distribution. The great majority of rock slope failures are ancient features, but debris flows and small translational slides in drift (both triggered mainly by intensive rainstorms) are much more frequent at present and cause much greater damage, particularly to communications.     

Roman mining on Exmoor: a geomorphological approach at Anstey's Combe,Dulverton

Abstract

A survey of valley fills in south-facing combes (headwater valleys) along the south side of the Exmoor massif revealed an anomalously deep infill in one valley. This infill of up to 5 m depth had been gullied revealing a complex stratigraphy. Studies of the stratigraphy, clast orientation and shape suggested several accumulation episodes under different environmental conditions commencing in a periglacial climatic regime. Later units included sandy silts which can be dated using optically stimulated luminescence (OSL) of quartz grains. The OSL dates, indicate that the inter-gravel silts accumulated in two periods, the Romano-British period and the 16th–17th centuries AD. A survey of the very small valley catchment revealed a linear trench of a type associated with early iron mining. Given the anomalously high volume of accumulated sediment from such a small catchment and evidence of mining on the slope above the site, the geomorphic mechanism is almost certainly the downslope transport of mining debris from the slope to the valley floor. This study suggests that the systematic survey of headwater valleys in metalliferous uplands may be one way of locating areas of early mining activity and that such deposits could provide a chronology of working and abandonment.     

Scottish landform examples 44: the Dirc Mhòr meltwater gorge

The Dirc Mhòr gorge in the central Grampian Highlands is 1.1 km long, ～250 m wide and up to 110 m deep, and is incised in granite bedrock. It is the largest of several bedrock gorges that are incised into spurs, cols or plateau margins in the area, and its present catchment area is negligible. The floor of the gorge is covered by coarse rockfall debris, and the sides of the gorge are mantled by talus accumulations; surface water flow is absent. The gorge is inferred to have evolved over several glacial-interglacial cycles, with subglacial meltwater erosion deepening the gorge under successive ice sheets, and paraglacial rockwall collapse widening the gorge during intervening interglacial periods. Subglacial erosion may also have contributed to gorge enlargement as it widened.     

Oligocene-Miocene calcareous nannofossils from the Torquay Basin,Victoria, Australia

Oligocene-Miocene rocks of the Torquay Basin contain at least 55 different species of calcareous nannofossils. These species allow zonation of an offshore subsurface section (Nerita No. 1 Well) and two onshore sections (near Torquay). The Angahook Formation and the base of the Jan Juc Formation in the Nerita No. 1 Well belong to Martini's (1971) NP 22 calcareous nannofossil Zone (early Oligocene). The NP 23 Zone could not be identified with certainty, but Zones NP 24/25 (late Oligocene) to NN 2 (early Miocene) were recognized in the Jan Juc Formation. The Oligocene-Miocene boundary is present between 122 m and 135 m below the sea floor at this site. The Puebla Formation, exposed at the sea floor, contains NN 5 spanning the early-middle Miocene boundary.

Onshore along the Torquay coast, NP 24/25 (late Oligocene) is present in the Angahook Formation; the Jan Juc Formation at Bird Rock also contains NP 24/25, except the uppermost 2.5 m which belongs to NN 1. The NN 2 Zone begins at the contact between the Jan Juc and Puebla Formations and continues upward for at least 3 m. After a covered interval, NN 4 was identified 10 m above the contact. The Oligocene-Miocene boundary is placed at the base of the hard band capping Bird Rock in the type section of the Jan Juc Formation.

Nannofossil assemblages in the Torquay sections suggest deposition in cool, shallow continental shelf waters. The assemblages in Nerita No. 1 Well also suggest cool shelf waters, although deeper than at Torquay.     

An Examination of Vertical Accretion of Floodplain Sediments in the Labasa River Sugarcane Belt of Northern Fiji: Rates,Influences and Contributing Processes

The ¹³⁷Cs (caesium‐137) method was used to investigate medium‐term rates of sediment deposition on the floodplain of the Labasa River, on Vanua Levu island in northern Fiji. The Labasa basin is commercially important for sugarcane farming, which provides much revenue and sustains the economy in the greater Labasa area. Alluvium was sampled at three riverbank sites in vertical increments of 30 mm. Measured net vertical accretion rates, based on analysis of depth‐profiles of ¹³⁷Cs activity, ranged from 10 mm yr^?1 at a low‐lying site near a tributary confluence with the main river, to 60 mm yr^?1 on a levée that was elevated slightly above the adjacent floodplain. These rates of accretion are high, but in general agreement with rates recorded using similar methods in other tropical Pacific island river systems. Soil erosion under sugarcane on hilly parts of the lower Labasa basin is an important factor in rapid floodplain development. Observations made during Cyclone Ami, which traversed Vanua Levu island in early 2003, illustrate the major contribution of severe storm events to floodplain sediment supply, by triggering numerous landslides on catchment slopes and in‐channel debris floods, and by generating large‐magnitude overbank floods.     

重庆大足石刻舒成岩砂岩本体表面风化产物研究

针对重庆大足舒成岩摩崖造像和岩体富集灰尘部位出现的粉化伴随着层状剥落现象,采用X-射线衍射仪(XRD)、X-射线荧光光谱仪(XRF)、傅里叶变换红外光谱仪(FTIR)、环境扫描电子显微镜(SEM)和X-射线光电子谱(XPS)对岩石、岩体风化产物与灰尘样品进行了组成结构表征研究。研究发现灰尘和有害气体干沉降过程中酸性物质能够导致砂岩中钙质胶结物发生溶解,伴随着各种盐类结晶应力,导致岩石表层发生风化。研究成果为西南地区石窟寺保护提供了重要参考数据。     

Late Triassic palynoflora from the Pranhita–Godavari Valley,India: evidence from vertebrate coprolites

Vijaya, Prasad, G.V.R. & Singh, K., June, 2009. Late Triassic palynoflora from the Pranhita–Godavari Valley, India: evidence from vertebrate coprolites. Alcheringa 33, 91–111. ISSN 0311-5518.

The Upper Triassic Maleri Formation, represented by red clays and sandstones, has to date not produced any plant macrofossils or palynomorphs. Many spiral and non-spiral coprolites collected during this study from the Maleri Formation of the Pranhita-Godavari Valley were analysed for palynomorphs. Based on shape, nature of coiling and size, the Maleri coprolites are classified into seven groups. Of these, only Group-I, Type 5 (non-spiral) and amphipolar (spiral) types yielded diverse gymnospermous and pteridophytic spores, pollen, other plant debris and sparse fungal spores and algal remains. Occurrences of Antulsporites varigranulatus, Aratrisporites spp., Cadargasporites baculatus, Dubrajisporites isolatus, Enzonalasporites vigens, Foraminisporis coelatus, Grandispora spinosa, Kraeuselisporites saeptatus, Polycingulatisporites reduncus, Staurosaccites spp., Tethysispora unica and Tikisporites balmei confirm a Late Triassic age for the coprolite-bearing red clays. Records of Classopollis classoides and Callialasporites turbatus/dampieri in these assemblages more precisely suggest a Norian to Rhaetian age. The non-spiral coprolites were possibly produced by aquatic piscivorous animals whereas the spiral coprolites may have been produced by an as yet unidentified fish taxon. The coprolite-producing animals (spiral and non-spiral groups) possibly ingested gymnospermous and pteridophytic plant remains passively along with water or their herbivorous prey.