Thesis (Ph.D.) - University of St Andrews, November 2008.

The influence of seasonal influx of supraglacial meltwater on basal water pressures and consequent changes in ice surface velocity has been a focus of research spanning over three decades, particularly focussing on alpine glaciers. Now, with increased recognition for a need to better include glacial hydrology within models of ice dynamics and ice sheet evolution, the ability to predict where and when meltwater is delivered to the subglacial system is paramount, both for understanding the dynamics of alpine glaciers, and of large Arctic ice masses. Studies of the dynamics of outlet glaciers on the Greenland Ice Sheet have received particular attention in recent years, as links between ice acceleration and increased surface melt production are explored. Responses of horizontal and vertical ice velocities to meltwater generated suggest efficient transmission of meltwater from the supraglacial to subglacial hydrological systems. Indeed, in the case of meltwater transfer through the drainage of supraglacial lakes, it has been shown that such build-ups of stored meltwater can force crevasse penetration through many hundreds of metres of ice. This thesis presents a new modelling routine for the prediction of moulin formation and delivery of meltwater to the ice-bed interface. Temporal and spatial patterns of moulin formation through propagation of crevasses and drainage of supraglacial lakes are presented, and quantitative controls on water-driven crevasse propagation are investigated through a series of sensitivity tests. The model is applied to two glacial catchments: the Croker Bay catchment of Devon Ice Cap in High Arctic Canada; and Leverett Glacier catchment of the southwest Greenland Ice Sheet. Through model application to these sites, sensitivities to crevasse surface dimensions, ice tensile strength, ice fracture toughness and enhanced production of surface meltwater are investigated. Model predictions of moulin formation are compared with field observations and remotely sensed data, including ice surface velocities, dynamic flow regimes, and visible surface features. Additionally, model quantification of meltwater delivered to the ice-bed interface of Leverett Glacier is compared with profiles of measured proglacial discharge. Moulin formation is predicted at increasingly high elevation with time into the ablation season in both4catchments, and furthermore, the model predicts an increase in both the number of moulins and the number of lake drainages in response to increased melt scenarios. Sensitivity testing confirms that the model is most sensitive to factors influencing the rate at which meltwater fills a crevasse, and results highlight the importance of accurate parameterisation of crevasse surface dimensions and the tensile strength of the ice. Further applications of the model are discussed, with a focus on incorporation into coupled models of glacial hydrology and dynamics, including larger scale ice sheet modelling. The inclusion of spatially distributed points of temporally varying meltwater delivery to the subglacial system is imperative to fully understand the behaviour of the subglacial drainage system. Furthermore, dynamic response to future climatic change and increased melt scenarios, and the consequent evolution of ice masses, including those in the Canadian Arctic and Greenland, cannot be fully understood without first understanding the glacial hydrological processes driving many of these changes.

In this study we assessed growth laws of sub-delta crevasses in the Mississippi River delta plain, experimental laboratory deltas, and compared them to previously studied river dominated large deltas worldwide. Metrics for channel and delta geometry for each system were obtained using a combination of geospatial tools, bathymetric datasets, sediment size, and hydrodynamic observations. Most crevasses and experimental deltas appear to obey delta growth laws suggesting that they exhibit planform metrics similar to larger deltas. However, some channels within each system, exhibit outlier behavior (e.g. asymmetric growth) where channel length is much larger than channel width. Hydrodynamic observations and morphodynamic modeling results, support the role of confinement in governing this response, through direct lateral confinement of the receiving basin width and depth thus guiding channels, and indirect confinement caused by sediment cohesion, whereby natural levees guide the systems asymmetric channel growth.

Understanding the formation mechanics of glacial crevasses is crucial in a variety of glacial applications. Besides being a serious safety hazard during field campaigns, crevasses influence calving rates, mass balance, and the hydrological network of glaciers. Therefore, knowledge about their spatial distribution and potential development zones is highly beneficial. In this project, spatial distribution of surface crevasses on the Svalbard archipelago is investigated using a simple crevasse depth model, so called Nye’s zero-stress model, and a set of surface ice velocity data. The model is run for various ice temperatures as it is one of the parameters affecting crevasse development. The crevasse occurrences are also mapped and digitised manually using high resolution remote-sensed images. A special emphasis is put on the Lomonosovfonna ice cap, central Spitsbergen, where the crevasse distribution is studied in detail. The results indicate the greatest density of crevasses in regions of high ice surface velocity and concurrently high strain rates. These areas encompass mainly fast-flowing outlet valley glaciers, while the more stagnant ice caps and ice fields are characterised by little to no crevassing except for their margins. The modelled spatial distribution is concurrent with the observations, particularly for certain ice temperatures, highlighting the importance of accurate ice temperature measurements in modelling and a need of separation of the accumulation and ablation zones. Overall, the Nye’s zero-stress model yields accurate results and proves to be a suitable tool for the task. With room for fine-tuning, it is a promising tool that is easy to incorporate in other models.

Majoriteten av geomorfologin i Sveriges landskap är produkten av den senaste nedisningen som avslutades för ca 8000 år sedan. De Geer-morän är en typ av moränavlagring som härstammar från denna nedisning. De Geer-moränavlagringarna har ett omdebatterat bildningssätt samt är landformer med en omtvistad innebörd i landskapen världen över. Vad är det som moränavlagringarna återspeglar? Är det avlagringar från svämmande glaciärer, avlagringar formade vid grundstötningslinjen för en ryckvis avsmältande glaciär eller kanske avlagringar bildade av sammanpressat material i basala sprickor hos en glaciär? Diskussionen om De Geer-moränen har varit långvarig och teorierna är många. Här är forskningen inte överens. Det förefaller också att studerad De Geer-morän på olika platser världen över inte nödvändigtvis behöver ha haft samma bildningsätt. I Sverige förekommer De Geer-morän främst i två områden, längs med kusten i Norrbotten och Västerbotten, samt vid den mellansvenska israndzonen. I dessa områden förekommer moränavlagringarna som små ryggar i svärmar med några meters höjd. De studier som gjorts i Sverige om De Geer-morän har förklarligt nog tenderat att fokusera på dessa två större områden. Men, utöver dessa två större områden finns det också ett mycket mindre område beläget längs med Sveriges västkust, ett område med samma typ av moränavlagringar. De Geer-moränen här, benämnda Hallands kustmorän, är både äldre och färre, dessutom är senaste nedisningens avsmältning i detta område mer ovisst. I denna uppsats gjordes ett försök till att övergripligt redogöra för några av de presenterade teorierna som föreligger De Geer-moränens bildningssätt. Uppsatsen syftar till att studera och kartera De Geer-moränen belägen längs med Sveriges västkust med hjälp av höjddata och sedan jämföra dessa avlagringar med den teori som presenteras i bakgrunden för denna uppsats. De Geer-moränen kommer även att jämföras med en isavsmältningsrekonstruktion gjord i programmet ICESHEET 1.0, med lokala karterade isräfflor i området samt även analyseras utifrån beskrivningarna till SGUs utgivna jordartskartor. Förhoppningen var att denna uppsatsen skulle kunna bringa mer klarhet om omfattningen och utbredningen av De Geer-moränen längs med Sveriges västkust. Resultatet som erhölls presenterades bland annat visuellt med framtagna kartbilder. Några av de slutsatser som kunde dras utifrån denna studie var att De Geer-moränen längs med Sveriges västkust är starkt påverkade av svallning och överlagring av yngre sediment vilket gjorde dem svåra att upptäcka i landskapet. Högst troligt är det att förekomsten av De Geer-morän längs med Sveriges västkust är större än vad som syns vid dagens marknivå på grund av överlagring, dessutom tyder mycket på att avlagringarna fortsätter ut i Kungsbackafjorden och Kattegatt. Det gick för det studerade området att se att det fanns ett samband mellan jorddjup och förekomsten av De Geer-morän. Ryggarna var främst avlagrade ovanpå drumliner och förekom främst i områden med ett jorddjup på ≥ 5m. Det gick inte att dra några slutsatser om De Geer-moränens bildningssätt i området. / Most of the geomorphology in the Swedish landscape is a product of the last deglaciation that ended about 8000 years ago. De Geer moraine is moraine deposits that has debated origins as well as debated implications worldwide. What message does the deposits send? What kind of conditions do they reflect? Are they perhaps the deposits of surging glaciers, or deposits formed at the grounding lines of melting glaciers or perhaps are they squeezed ridges formed in basal crevasses of glaciers? The discussion in research worldwide about the origin of these features have been going on for a long time and there is a lot of different theories about how the deposits are formed. The De Geer moraines in Sweden are mainly located in two larger areas, one of them being along the east coast in Norrbotten and Västerbotten, and the other one being a large belt of deposits that are located parallel to the big Swedish lake Vänern. The majority of the published articles about De Geer moraine in Sweden are therefore understandably about these two larger areas, however there are also a much smaller area of De Geer moraine along Sweden’s west coast. These deposits are called Halland’s coastal moraines and are not studied to the same extent as the other two areas. This bachelor thesis aims to, in a general way, describe some of the different theories there are about the formation of these ridges. The purpose of this thesis is to study and map the De Geer moraine along the Swedish west coast and compare them to the theory featured in the background of this paper. The ridges will then also be studied on the basis of a glacier melting reconstruction in the computer software ICESHEET 1.0, of ice striations in the area and lastly on the basis of the descriptions to the quaternary maps published by Geological Survey of Sweden. Hopefully, this paper will bring some clarity about the De Geer moraine ridges along the Swedish west coast. The results from this thesis were presented visually in different types of map sheets. Some of the conclusions that could be drawn from this bachelor thesis was that ridges along the Swedish west coast were both wave-washed and superimposed by younger sediments which therefore made them hard to both map and distinguish. There is a high probability that the occurrence of De Geer moraine is much larger in the area than what could be seen at today’s ground level. Also, the distribution of the ridges suggested that they continued out in Kattegatt and the Kungsbackafjord. In general, the ridges were superimposed on drumlins and there was shown to be a connection between soil depth and the occurrence of De Geer moraine, the ridges mainly occurred where the soil depth were ≥5 metres. Despite of this, no conclusion could be drawn about the formation of the features.