John K. Hillier

Global distribution of seamounts from ship‐track bathymetry data

km of ship tracks to find 201,055 probableseamounts,anorderofmagnitudemorethanpreviouscountsacross a wider height-range (0.1 < h < 6.7 km). In the NorthPacific, seamounts’ spatial distribution substantially reflectsridge-crest conditions, variable on timescales of 10 s of Maand along-ridge distances of 1,000 km, rather than intra-plate hot-spot related volcanic activity. In the Atlantic,volcano numbers decrease, somewhat counter-intuitively,towards Iceland suggesting that abundant under-ridge meltmay deter the formation of isolated volcanoes. Neitherpreviously used empirical curve (exponential or power-law)describes the true size-frequency distribution of seamounts.Nevertheless, we predict 39 ± 1 10

Manual mapping of drumlins in synthetic landscapes to assess operator effectiveness

Mapped topographic features are important for understanding processes that sculpt the Earths surface. This paper presents maps that are the primary product of an exercise that brought together 27 researchers with an interest in landform mapping wherein the efficacy and causes of variation in mapping were tested using novel synthetic DEMs containing drumlins. The variation between interpreters (e.g. mapping philosophy, experience) and across the study region (e.g. woodland prevalence) opens these factors up to assessment. A priori known answers in the synthetics increase the number and strength of conclusions that may be drawn with respect to a traditional comparative study. Initial results suggest that overall detection rates are relatively low (34–40%), but reliability of mapping is higher (72–86%). The maps form a reference dataset.

Exploring Explanations of Subglacial Bedform Sizes Using Statistical Models

Sediments beneath modern ice sheets exert a key control on their flow, but are largely inaccessible except through geophysics or boreholes. In contrast, palaeo-ice sheet beds are accessible, and typically characterised by numerous bedforms. However, the interaction between bedforms and ice flow is poorly constrained and it is not clear how bedform sizes might reflect ice flow conditions. To better understand this link we present a first exploration of a variety of statistical models to explain the size distribution of some common subglacial bedforms (i.e., drumlins, ribbed moraine, MSGL). By considering a range of models, constructed to reflect key aspects of the physical processes, it is possible to infer that the size distributions are most effectively explained when the dynamics of ice-water-sediment interaction associated with bedform growth is fundamentally random. A ‘stochastic instability’ (SI) model, which integrates random bedform growth and shrinking through time with exponential growth, is preferred and is consistent with other observations of palaeo-bedforms and geophysical surveys of active ice sheets. Furthermore, we give a proof-of-concept demonstration that our statistical approach can bridge the gap between geomorphological observations and physical models, directly linking measurable size-frequency parameters to properties of ice sheet flow (e.g., ice velocity). Moreover, statistically developing existing models as proposed allows quantitative predictions to be made about sizes, making the models testable; a first illustration of this is given for a hypothesised repeat geophysical survey of bedforms under active ice. Thus, we further demonstrate the potential of size-frequency distributions of subglacial bedforms to assist the elucidation of subglacial processes and better constrain ice sheet models.

Structural properties of mobile armors formed at different flow strengths in gravel-bed rivers

Differences in the structure of mobile armors formed at three different flow strengths have been investigated in a laboratory flume. The temporal evolution of the bed surfaces and the properties of the final beds were compared using metrics of surface grain size, microtopography, and bed organization at both grain and mesoscales. Measurements of the bed condition were obtained on nine occasions during each experiment to describe the temporal evolution of the beds. Structured mobile armors formed quickly in each experiment. At the grain scale (1–45 mm; 9 ≤ Ds50 ≤ 17 mm where Ds50 is the median surface particle size), surface complexity decreased and bed roughness increased in response to surface coarsening and the development of the mobile armor. Particles comprising the armor also became flow aligned and developed imbrication. At a larger scale (100–200 mm), the surface developed a mesoscale topography through the development of bed patches with lower and higher elevations. Metrics of mobile armor structure showed remarkable consistency over prolonged periods of near-constant transport, demonstrating for the first time that actively transporting surfaces maintain an equilibrium bed structure. Bed structuring was least developed in the experiments conducted at the lowest flow strength. However, little difference was observed in the structural metrics of the mobile armors generated at higher flows. Although the range of transport rates studied was limited, the results suggest that the structure of mobile armors is insensitive to the formative transport rate except when rates are low (τ* ≈ 0.03 where τ* is the dimensionless shear stress).

Counting better? An examination of the impact of quantitative method teaching on students’ statistical anxiety and confidence to complete statistical tasks.

This article reports the results of research concerned with students’ statistical anxiety and confidence to both complete and learn to complete statistical tasks. Data were collected at the beginning and end of a quantitative method statistics module. Students recognised the value of numeracy skills but felt they were not necessarily relevant for graduate employability and preferred to study with words rather than numbers. A significant reduction in anxiety and increase in confidence to complete statistical tasks were found. Students seemed to feel more confident about doing and learning less complex procedures. Results reinforce the need to provide students with additional mathematical and statistical support outside of quantitative method courses as well as that numeric learning materials and study tasks need to be embedded across the curriculum within substantive disciplinary modules. The design of numeric study tasks needs to be carefully considered to ease the transition for students from simple to more complex statistical procedures while simultaneously reinforcing the importance of numeracy skills for examining substantive disciplinary topics and promoting graduate employability.

Counting better? An examination of the impact of quantitative method teaching on statistical anxiety and confidence

This article reports the results of research concerned with students’ statistical anxiety and confidence to both complete and learn to complete statistical tasks. Data were collected at the beginning and end of a quantitative method statistics module. Students recognised the value of numeracy skills but felt they were not necessarily relevant for graduate employability and preferred to study with words rather than numbers. A significant reduction in anxiety and increase in confidence to complete statistical tasks were found. Students seemed to feel more confident about doing and learning less complex procedures. Results reinforce the need to provide students with additional mathematical and statistical support outside of quantitative method courses as well as that numeric learning materials and study tasks need to be embedded across the curriculum within substantive disciplinary modules. The design of numeric study tasks needs to be carefully considered to ease the transition for students from simple to more complex statistical procedures while simultaneously reinforcing the importance of numeracy skills for examining substantive disciplinary topics and promoting graduate employability.

Comment on "mantle flow drives the subsidence of oceanic plates"

Adam and Vidal (Reports, 2 April 2010, p. 83) reported sea-floor depth increasing as the square root of distance from the ridge along “mantle flow lines.” However, their data actually support a depth-age relationship and “flattening” at older ages. We argue that no plausible physical mechanism supports their proposal that mantle flow drives subsidence.

Submarine Geomorphology: Quantitative Methods Illustrated with the Hawaiian Volcanoes

Abstract Submarine geomorphology, like sub-aerial geomorphology, is the study of the Earths surface in order to better understand tectonic and geomorphic processes. Such processes include volcanism, neo-tectonics (i.e. the activity of geological faults), the escape of hydrocarbons and submarine erosion (e.g. by channel cutting or landslides). Furthermore, submarine geomorphology can provide valuable input into other fields, such as indicating likely fisheries or habitats for corals. This case study illustrates quantitative methods in submarine geomorphology with ‘Regional–Residual Relief Separation’, which splits landscapes (digital elevation models) into two components, isolating features of interest in one component for visualisation or analysis as desired: here, isolating Hawaiian volcanoes. Mapping volcanoes and accurately quantifying descriptive properties such as height and volume are vital to constrain our understanding of how the Earth melts and volcanoes erupt. Key future opportunities in submarine geomorphology using quantitative methods are also highlighted.

Production and preservation of the smallest drumlins

Abstract Few very small drumlins are typically mapped in previously glaciated landscapes, which might be an important signature of subglacial processes or an observational artefact. One hundred and forty-three newly emergent drumlins, recently sculpted by the Múlajökull glacier, have been mapped using high-resolution LiDAR and aerial photographs in addition to field surveying. In this paper, these are used as evidence that few small drumlins (e.g., height H 4 m, width W 40 m, length L 100 m) are produced; at least, few survive to pass outside the ice margin in this actively forming drumlin field. Specifically, the lack of a multitude of small features seen in other landforms (e.g., volcanoes) is argued not to be due to (i) Digital Elevation Model resolution or quality, (ii) mapper ability in complex (i.e., anthropogenically cluttered or vegetated) landscapes or (iii) post-glacial degradation at this site. So, whilst detection ability must still be at least acknowledged in drumlin mapping, and ideally corrected for in quantitative analyses, this observation can now be firmly taken as a constraint upon drumlin formation models (i.e., statistical, conceptual or numerical ice flow). Our preferred explanation for the scarcity of small drumlins, at least at sites similar to Múlajökull (i.e., ice lobes with near-margin drumlin genesis), is that they form stochastically during multiple surge cycles, evolving from wide and gentle pre-existing undulations by increasing rapidly in amplitude before significant streamlining occurs.

Comparing threshold definition techniques for rainfall induced landslides: a national assessment using radar rainfall

Translational landslides and debris flows are often initiated during intense or prolonged rainfall. Empirical thresholds aim to classify the rain conditions that are commonly associated with landslide occurrence and therefore improve understating of these hazards and predictive ability. Objective techniques that are used to determine these thresholds are likely to be affected by the length of the rain record used, yet this is not routinely considered. Moreover, remotely sensed spatially continuous rainfall observations are under-exploited. This study compares and evaluates the effect of rain record length on two objective threshold selection techniques in a national assessment of Scotland using weather radar data. Thresholds selected by ‘threat score’ are sensitive to rain record length whereas, in a first application to landslides, ‘optimal point’ (OP) thresholds prove relatively consistent. OP thresholds increase landslide detection and may therefore be applicable in early-warning systems. Thresholds combining 1- and 12-day antecedence variables best distinguish landslide initiation conditions and indicate that Scottish landslides may be initiated by lower rain accumulation and intensities than previously thought.