Using UAV acquired photography and structure from motion techniques for studying glacier landforms: application to the glacial flutes at Isfallsglaciären

Glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small-scale fragile geomorphological features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor–relief landforms as wind, weather, water and vegetation impacts on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close-range aerial photography of the foreland of Isfallsglaciären, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2 cm horizontal resolution were created from this photography using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss-side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore, the size of this boulder was found to strongly correlate with the width and relief of the lee-side flute. This is consistent with the lee-side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study.

The Terrace Structure: Trenches I, II and XV

The Settlement at Dhaskalio is the first volume in the series The Sanctuary on Keros: Excavations at Dhaskalio and Dhaskalio Kavos, 2006-2008, edited by Colin Renfrew, Olga Philaniotou, Neil Brodie, Giorgos Gavalas and Michael Boyd. Here the findings are presented from the well-stratified settlement of Dhaskalio, today an islet near the Cycladic island of Keros, Greece. A series of radiocarbon dates situates the duration of the settlement from around 2750 to 2300 BC. The volume begins with a discussion of the geological setting of Keros and of sea-level change, concluding that Dhaskalio was in the third millennium BC linked to Keros by a narrow causeway. The excavation and finds (excluding the pottery, discussed in later volumes) are fully documented, with consideration of stratigraphy, geomorphology, organic remains, and the evidence for metallurgy. It is concluded that there was a small permanent population of around 20, increased periodically by up to 400 visitors who would have participated in the rituals of deposition occurring at the Sanctuary at Kavos, situated opposite, on Keros itself, for which the detailed evidence (including abundant fragmented pottery, marble vessels and sculptures) will be presented in Volumes II and III

Stone temperature and moisture variability under temperate environmental conditions: implications for sandstone weathering

Temperature and moisture conditions are key drivers of stone weathering processes in both natural and built environments. Given their importance in the breakdown of stone, a detailed understanding of their temporal and spatial variability is central to understanding present-day weathering behaviour and for predicting how climate change may influence the nature and rates of future stone decay.
Subsurface temperature and moisture data are reported from quarry fresh Peakmoor Sandstone samples exposed during summer (June–July) and late autumn / early winter (October–December) in a mid-latitude, temperate maritime environment. These data demonstrate that the subsurface thermal response of sandstone comprises numerous short-term (minutes), low magnitude fluctuations superimposed upon larger-scale diurnal heating and cooling cycles with distinct aspect-related differences. The short-term fluctuations create conditions in the outer 5–10 mm of stone that are much more ‘energetic’ in comparison to the more subdued thermal cycling that occurs deeper within the sandstone samples.
Data show that moisture dynamics are equally complex with a near-surface region (5–10 mm) in which frequent moisture cycling takes place and this, combined with the thermal dynamism exhibited by the same region may have significant implications for the nature and rate of weathering activity. Data indicate that moisture input from rainfall, particularly when it is wind-driven, can travel deep into the stone where it can prolong the time of wetness. This most often occurs during wetter winter months when moisture input is high and evaporative loss is low but can happen at any time during the year when the hydraulic connection between near-surface and deeper regions of the stone is disrupted with subsequent loss of moisture from depth slowing as it becomes reliant on vapour diffusion alone.
These data illustrate the complexity of temperature and moisture conditions in sandstone exposed to the ‘moderate’ conditions of a temperate maritime environment. They highlight differences in thermal and moisture cycling between near-surface (5–10 mm) and deeper regions within the stone and contribute towards a better understanding of the development of structural and mineralogical heterogeneity between the stone surface and substrate.

Sedimentology, structure and age estimate of five continental slope submarine landslides, eastern Australia

Sedimentological and accelerator mass spectrometry (AMS) 14C data provide estimates of the structure and age of five submarine landslides (∼0.4–3 km3) present on eastern Australia's continental slope between Noosa Heads and Yamba. Dating of the post-slide conformably deposited sediment indicates sediment accumulation rates between 0.017 m ka–1 and 0.2 m ka–1, which is consistent with previous estimates reported for this area. Boundary surfaces were identified in five continental slope cores at depths of 0.8 to 2.2 m below the present-day seafloor. Boundary surfaces present as a sharp colour-change across the surface, discernible but small increases in sediment stiffness, a slight increase in sediment bulk density of 0.1 g cm–3, and distinct gaps in AMS 14C ages of at least 25 ka. Boundary surfaces are interpreted to represent a slide plane detachment surface but are not necessarily the only ones or even the major ones. Sub-bottom profiler records indicate that: (1) the youngest identifiable sediment reflectors upslope from three submarine landslides terminate on and are truncated by slide rupture surfaces; (2) there is no obvious evidence for a post-slide sediment layer draped over, or burying, slide ruptures or exposed slide detachment surfaces; and (3) the boundary surfaces identified within the cores are unlikely to be near-surface slide surfaces within an overall larger en masse dislocation. These findings suggest that these submarine landslides are geologically recent (<25 ka), and that the boundary surfaces are either: (a) an erosional features that developed after the landslide, in which case the boundary surface age provides a minimum age for the landslide; or (b) detachment surfaces from which slabs of near-surface sediment were removed during landsliding, in which case the age of the sediment above the boundary surface indicates the approximate age of landsliding. While an earthquake-triggering mechanism is favoured for the initiation of submarine landslides on the eastern Australian margin, further evidence is required to confirm this interpretation.