Kevin P. Norton

Glacial conditioning as an erosional driving force in the Central Alps

Unparalleled data availability in the European Alps has led to an ongoing debate about the driving mechanism behind the concurrent patterns of surface denudation and modern rock uplift. Analysis of stream channels reveals that oversteepened stream segments are primarily located in landscapes with strong glacial inheritance. This leads to a transient signal in the landscape, with the result that erosion is spatially focused by a combination of glacial conditioning and lithologic controls. We postulate that the effect of glacial forcing is a positive feedback cycle between erosion and rock uplift, driving rapid rates of both in the Alpine landscape. This mechanism may explain the observed increases in sediment flux since the late Pliocene.

Migrating deformation in the Central Andes from enhanced orographic rainfall

Active shortening in the Central Andes shifted from the western to the eastern margin between 10-7 Ma. Here we propose that this shift was primarily controlled by changes in erosion patterns. The uplift of the Andes blocked easterly winds, resulting in enhanced orographic rainfall on the eastern margin and reduced rainfall on the western margin. Lower erosion rates, associated with the arid conditions, caused the western margin to steepen inhibiting internal deformation and the migration of deformation to the eastern margin where it is active today. River channel profiles on the western margin are indicative of long-term transience from an older tectonic event whereas those on the eastern margin reflect ongoing coupled climatic-tectonic feedback. Both critical wedge theory and local-scale fault friction calculations support this interpretation. This work emphasizes the role that orographic rainfall and erosion can have on the orogen-scale development of mountain belts.

Climatic Forcing on Channel Profiles in the Eastern Cordillera of the Coroico Region, Bolivia

Orographic precipitation has a large impact on channel morphology and rock uplift via a positive feedback to erosion. We show that in the Eastern Cordillera of Bolivia, channel concavities reach their highest values where annual precipitation increases in the downstream direction, exceeding 3000 mm. The steepest channels are upstream of this zone of high concavity, where precipitation rates are <1000 mm yr−1. Channels exhibit graded forms both upstream and downstream of this transient reach. We conclude that the prolonged effect of orographic erosion and related tectonic uplift is the preservation of channels with extreme concavities in the Eastern Cordillera.

Estimating permafrost distribution in the maritime Southern Alps, New Zealand, based on climatic conditions at rock glacier sites

Alpine permafrost occurrence in maritime climates has received little attention, despite suggestions that permafrost may occur at lower elevations than in continental climates. To assess the spatial and altitudinal limits of permafrost in the maritime Southern Alps, we developed and tested a catchment-scale distributed permafrost estimate. We used logistic regression to identify the relationship between permafrost presence at 280 active and relict rock glacier sites and the independent variables a) mean annual air temperature and b) potential incoming solar radiation in snow free months. The statistical relationships were subsequently employed to calculate the spatially-distributed probability of permafrost occurrence, using a probability of ≥ 0.6 to delineate the potential permafrost extent. Our results suggest that topoclimatic conditions are favorable for permafrost occurrence in debris-mantled slopes above ~ 2000 m in the central Southern Alps and above ~ 2150 m in the more northern Kaikoura ranges. Considering the well-recognized latitudinal influence on global permafrost occurrences, these altitudinal limits are lower than the limits observed in other mountain regions. We argue that the Southern Alps’ lower distribution limits may exemplify an oceanic influence on global permafrost distribution. Reduced ice-loss due to moderate maritime summer temperature extremes may facilitate the existence of permafrost at lower altitudes than in continental regions at similar latitude. Empirical permafrost distribution models derived in continental climates may consequently be of limited applicability in maritime settings.

Quantifying sediment supply at the end of the last glaciation: Dynamic reconstruction of an alpine debris-flow fan

In this paper we quantify the sediment dynamics in the formerly glaciated Zielbach catchment in the Italian Alps from the end of the Last Glacial Maximum (LGM) until today. As a basis for our quantification, we use the stratigraphic record offered by a 3.5 km2 large fan that we explore with a seismic survey, stratigraphic analyses of drillhole material, and 14C ages measured on organic matter encountered in these drillings. In addition, we calculate past denudation rate variability in the fan deposits using concentrations of cosmogenic 10Be. We merge this information into a scenario of how the sediment flux has changed through time and how this variability can be related to climatic variations, framed within well-known paraglacial models. The results document a highly complex natural system. From the LGM to the very early Holocene, ice-melted discharge and climate variability promoted a high sediment flux (sedimentation rate up to 40 mm/yr). This flux then dramatically decreased toward interglacial values (0.8 mm/yr at 5–4 calibrated kyr B.P.). However, in contrast to the trend of classic paraglacial models, the flux recorded at Zielbach shows secondary peaks at 6.5 ka and 2.5 ka, with values of 13 mm/yr and 1.5 mm/yr, respectively. Paleo-denudation rates also decrease from ∼33 mm/yr at the beginning of the Holocene to 0.42 mm/yr at 5 ka, with peaks of ∼6 mm/yr and 1.1 mm/yr at 6.5 ka and 2.5 ka. High-amplitude climate change is the most likely cause of the secondary peaks, but anthropogenic activities may have contributed as well. The good correlation between paleo-sedimentation and paleo-denudation rates suggests that the majority of the deglaciated material destocked from the Zielbach catchment is stored in the alluvial fan.

Reconstruction of a glacial lake outburst flood (GLOF) in the Engaño Valley, Chilean Patagonia: Lessons for GLOF risk management.

Floods from moraine-dammed lake failures can have long standing effects not only on riverine landscapes but also on mountain communities due to the high intensity (i.e. great depth and high velocities) and damaging capacity of glacial lake outburst floods (GLOFs). GLOFs may increase in frequency as glaciers retreat and new lakes develop and there is an urgent need to better understand GLOF dynamics and the measures required to reduce their negative outcomes. In Patagonia at least 16 moraine-dammed lakes have failed in historic time, however, data about GLOF dynamics and impacts in this region are limited. We reconstruct a GLOF that affected a small village in Chilean Patagonia in March 1977, by semi structured interviews, interpretation of satellite images and 2D hydraulic modelling. This provides insight into the GLOF dynamics and the planning issues that led to socioeconomic consequences, which included village relocation. Modelling shows that the water released by the GLOF was in the order of 12-13 × 10(6)m(3) and the flood lasted for about 10h, reaching a maximum depth of ~1.5m in Bahía Murta Viejo, ~ 26 km from the failed lake. The lake had characteristics in common with failed lakes worldwide (e.g. the lake was in contact with a retreating glacier and was dammed by a narrow-steep moraine). The absence of land-use planning and the unawareness of the GLOF hazard contributed to the village flooding. The Río Engaño GLOF illustrates how small-scale and short-distance migration is a reasonable coping strategy in response to a natural hazard that may increase in frequency as atmospheric temperature rises and glaciers retreat.

Timing the Interface Between Mass Wasting and Fluvial Processes with OSL

In this chapter, we present a successful application of optically-stimulated luminescence (OSL) dating for reconstructing Quaternary alluvial and colluvial terrace sequences in the Pisco valley of western Peru. Here, climate-driven changes in debris-flow activity resulted in sediment aggradation and subsequent dissection forming distinct terrace levels. The terraces are made up of rather well-sorted, polymict, clast-supported conglomerates at the base and monomict, matrix-supported breccias towards the top. Both the abundance and thicknesses of breccias increase upsection and form the top of each sequence, leading to fan-shaped geometries. The well-sorted and clast-supported fabric of the conglomerates is interpreted as deposition by the perennial braided Pisco trunk stream. In contrast, the matrix-supported breccias were deposited by debris-flows sourced locally in the adjacent tributary valleys. The superposition of breccias on conglomerates implies that tributary debris-flow fans prograded from the valley margin towards the centre. OSL dating reveals that initiation of sediment accumulation was concurrent with a shift to more humid conditions. OSL ages also show that sediment aggradation started at the valley outlet, with the locus of sediment deposition then propagating farther upstream. Subsequent erosion and dissection of the valley fill commenced later during the same humid interval and continued throughout the following drier climate. Interestingly, the destructive phases also started at the valley outlet and propagated upstream, presumably as the hillslope sediment reservoirs became depleted. It is concluded that the sedimentary fill of the Pisco valley, and presumably that in other mountain belts, records a transient, non-steady response of debris-flows and fluvial processes to climate change, where non-steady sediment flux by hillslope erosion is buffered for a limited time span.

Late holocene nearshore change at a nontidal transgressive systems tract strandplain complex, Presque Isle, Pennsylvania, U.S.A

Abstract Understanding coastal change at mesotimescales is a prerequisite for developing predictive coastal response models and remains a “holy grail” for coastal scientists and engineers. The historical behavior of the Presque Isle strandplain on the North American Great Lakes provides insight into the complexities of net coastal response to a large set of geoenvironmental variables. Principal among these variables are high-frequency lacustrine transgressions and regressions of up to 1 meter in magnitude that occur at timescales of years to decades against a backdrop of longer term transgression (8 mm/y, 1901–97). Almost a century of coastal processes and anthropogenic modifications have resulted in nearshore net accretion of 15.5 × 106 cubic meters (161 × 103 m3/y) for this terminal end of a 36-kilometer-long coastal sediment dispersal system. Sediment eroded from the strandplains updrift transgressive neck sector, coupled with additional inputs from mass wasting of an updrift bluff coast and beach nourishment, is dispersed primarily along-coast to build downdrift regressive shoreface and capping progradational strandplain depositional systems. Several general rules describe coastal change during quarter century–scale regressive and transgressive lake phases. The downdrift composite spit sector of Presque Isle is always accretional across the entire nearshore profile regardless of lake phase. The response of the updrift transgressive sector is highly variable, and shoreline recession occurs during both regressive and transgressive lake phases. During periods of minor forced regression (−2 mm/y), the Presque Isle nearshore undergoes moderate net erosion, whereas during major transgression (12–15 mm/y), it undergoes minor to major net accretion. In general, erosional and accretional areas migrate on-, off-, and alongshore because transgressive-regressive cycles influence the interaction of natural and anthropogenic sediment source environments with the wave field, which entrains and disperses sediment.

Past and present dynamics of Skelton Glacier, Transantarctic Mountains

Abstract Any future changes in the volume of Antarctica’s ice sheets will depend on the dynamic response of outlet glaciers to shifts in environmental conditions. In the Transantarctic Mountains, this response is probably heavily dependent on the geometry of the system, but few studies have quantified the sensitivity of these glaciers to environmental forcings. Here we investigated the controls, along-flow sensitivity and time-dependent dynamics of Skelton Glacier. Three key outcomes were: i) present-day flow is governed primarily by surface slope, which responds to reduced valley width and large bed undulations, ii) Skelton Glacier is more susceptible to changes in atmospheric temperature than precipitation through its effect on basal sliding near the grounding line, and iii) under conditions representative of Pliocene and Quaternary climates large changes in ice thickness and velocity would have occurred in the lower reaches of the glacier. Based on these new quantitative predictions of the past and present dynamics of Skelton Glacier, we suggest that similar Transantarctic Mountain outlet glaciers could experience greater ice loss in their confined, lower reaches through increased basal sliding and ocean melt under warmer-than-present conditions. These effects are greatest where overdeepenings exist near the grounding line.

An ice-rich flow origin for the banded terrain in the Hellas basin, Mars

The interior of Hellas Basin displays a complex landscape and a variety of geomorphological domains. One of these domains, the enigmatic banded terrain covers much of the northwestern part of the basin. We use high-resolution (Context Camera and High-Resolution Imaging Science Experiment) Digital Terrain Models to show that most of the complex viscous flowing behavior exhibited by the banded terrain is controlled by topography and flow-like interactions between neighboring banded terrain. Furthermore, the interior of the basin hosts several landforms suggestive of the presence of near-surface ice, which include polygonal patterns with elongated pits, scalloped depressions, isolated mounds, and collapse structures. We suggest that thermal contraction cracking and sublimation of near-surface ice are responsible for the formation and the development of most of the ice-related landforms documented in Hellas. The relatively pristine form, lack of superposed craters, and strong association with the banded terrain, suggest an Amazonian (<3 Ga) age of formation for these landforms. Finally, relatively high surface pressures (above the triple point of water) expected in Hellas and summertime temperatures often exceeding the melting point of water ice suggest that the basin may have recorded relatively “temperate” climatic conditions compared to other places on Mars. Therefore, the potentially ice-rich banded terrain may have deformed with lower viscosity and stresses compared to other locations on Mars, which may account for its unique morphology.