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Ice sheet interiors are conventionally regarded as non‐erosive. Yet subglacial conditions may be transformed during deglaciation by the arrival of large volumes of meltwater at the ice sheet bed. The development of a dynamic meltwater drainage system and the onset of basal sliding have potential to increase erosion rates in bedrock and sediment. Here, we examine the impact of late deglacial thawing on the Rogen plateau, located near the former ice divide of the Fennoscandian Ice Sheet. We provide new maps of glacial and glacifluvial landforms which we combine with existing data on Quaternary sediments and landforms. Cross‐cutting and overlapping relations allow for an event sequence to be established of the deglaciation period. In the Early Holocene (< 11 ka), an ice lobe onset zone developed at the Rogen plateau. In places where meltwater reached the bed and where pressures rose to overpressure, it caused fracture dilation in horizontally bedded sandstones and rock brecciation. The onset of sliding and application of drag resulted in the mobilization of bedrock sheets. The establishment of meltwater corridors led to fluidization of sediments at the bed, dissection and modification of ribbed moraines and formation of murtoos and hummock corridors. During final stagnation of the ice sheet, meltwater drained through channels forming axial eskers. Bedrock erosion during deglaciation reached depths up to 4 m, and in conjunction with some recycling of till, generated ~ 317 km2 of boulder cover. The average erosion depths by removal and reworking of sediment are ~ 0.9–1.1 m across areas below 900 m elevation. This study shows that when the cold‐based interiors of ice sheets become briefly activated by large subglacial meltwater delivery late in deglaciation, there can be significant reworking and erosion of rock and sediment. [ABSTRACT FROM AUTHOR]

The Arctic today has shallow, chemically immature, and frost-dominated weathering regimes. At Sokli, Finland (68°N), a 70 m deep palaeo-weathering profile is developed in a Devonian carbonatite pipe that represents fundamentally different past weathering environments. Formation of the apatite-francolite P-ore likely began under Palaeogene warm, humid climates. Later, cryptomelane (K-Mn oxide) crusts developed within the ore that have yielded peak 40Ar/39Ar ages of 16.20 ± 0.13 Ma (2σ)., The crusts formed at the redox front during the Miocene Climatic Optimum (∼16.9–14.7 Ma) under mean annual temperatures ∼12–14 °C warmer than today. The presence of the cryptomelane crust at shallow depth (15 m) indicates very low erosion rates since formation, consistent with its position on a tectonically stable Archaean craton and in the cold-based ice-divide zone of successive Fennoscandian ice sheets. The Miocene Climatic Optimum triggered a pulse of intensive weathering in mid- and low latitudes; the Sokli cryptomelane ages demonstrate that intensive chemical weathering extended into the Arctic. • Intensely weathered Devonian carbonatite in northern Finland. • 40Ar/39Ar dating of supergene cryptomelane to Miocene Climatic Optimum. • First indication that global Miocene weathering pulse extended into the Arctic. • Fundamental shifts may be underway in Arctic weathering systems. [ABSTRACT FROM AUTHOR]

Abstract: The buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier Equilibrium Line Altitudes (ELAs), irrespective of uplift rates, rock type or pre-existing topography. Here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and ELAs, and whether the glacial system can produce low-relief surfaces or limit summit heights. Plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited, pre-glacial relief. Summit heights may correlate with ELAs but no causal link need be implied as summit erosion rates are low, cirque headwalls may not directly abut summits and, on passive margins, cirques are cut into pre-existing mountain topography. Any simple links between ELAs and glacial erosion break down on passive margins due to topographic forcing of ice-sheet growth, and to the km-scale vertical swaths through which ELAs have shifted through the Quaternary. Glaciers destroy rather than create low-relief rock surfaces through the innate tendency for ice flow to be faster, thicker and warmer along valleys. The glacial buzzsaw cuts down. [Copyright &y& Elsevier]

We investigate the long-term geomorphological evolution of the inselberg plains on the glaciated northern Fennoscandian shield. The shield surfacehas been largely stripped of pre-Quaternary correlative sediments and saprolites by non-glacial and glacial erosion, which make investigations of pre-Quaternary landscape development a challenge. The relief of the study area, covering 33,000 km2 in the centre of the shield in northern Sweden, includes an abundance of inselbergs that provide the basis for the study. We examine the relief of the inselberg plains, integrated with glacial-geomorphologic features, geology, and weathering remnants, by using GIS-analysis and fieldwork. Several key areas are used to demonstrate the impact of glaciations on the large-scale relief, and the influence of geology, structure and deep weathering on relief formation. Glacial erosion had only a minor impact on the large-scale bedrock morphology of northern Sweden. Based on excavations and observations in the Parkajoki area, an area largely preserved under cold-based ice during Quaternary glaciations, we infer that grus weathering, resulting in saprolite covers of up to 10-20 m thickness, occurred in the Neogene. However, inselbergs are considerably higher than that, and must therefore be the result of older deep weathering and erosional events. Narrow fracture zones associated with deep kaolins found in northern Fennoscandia may represent the roots of older generations of deep weathering covers but their age and formation is yet unclear. The geology of the area has greatly influenced the present surface relief. The positions and footprints of the inselbergs are often closely controlled by bedrock type and fracturing. Granite inselbergs generally have dome forms where dome shape and slopes are determined by joint patterns. Steps between palaeosurfaces locally coincide with lithological boundaries and major faults. These links indicate the fundamental importance of etch processes in shaping the relief through multiple cycles of deep weathering and stripping. Palaeosurfaces have been extended and lowered through time, with isolation of small inselbergs during erosion of higher palaeosurfaces. The timescales for relief generation remain uncertain and there is a pressing need to understand the significance of and to date the sediments, saprolites and weathered ore bodies that rest on the surface of the northern Fennoscandian shield. [ABSTRACT FROM AUTHOR]

Abstract: The Grind of the Navir is an ignimbrite headland on the exposed Atlantic coast of the Shetland Islands, Scotland. During storms, offshore wave heights exceed 20 m and deep water close inshore allows high-energy waves to impact on these cliffs. The cliff top at ∼15 m above sea level is awash with wave water when wave heights exceed 8 m, a condition met in storms in most years. Detailed mapping, ground photography and patterns of lichen colonisation and growth allow the processes, patterns and rates of erosion to be assessed on different parts of the headland over the past 100 years. Recent fractures in the rock of the cliff face and top indicate that wave impact forces exceed the 1.5 kPa tensile strength of the rock and fresh sockets low on the cliff face record the removal of fracture-bounded blocks that are lost to seaward. On the upper part of the cliff face, upward moving water flow is capable of removing blocks from both vertical faces and stepped overhangs. Clefts in the cliff face are extended inwards and upwards by crack propagation and block removal, leading to the development of slot caves. The movement of waves across the cliff top in fast-moving bores quarries blocks from the cliff face close to the edge and from rock steps on the cliff top, promoting further rock fracturing. Socket sizes and block characteristics indicate that blocks of >1 m3 are rotated from sockets on the cliff top platform and carried landwards for up to 60 m to be deposited in a series of boulder ridges on the cliff top. Multiple boulder movements during a storm in January 2005 generated impact marks and orientated striations that allow the pattern of water movement to be reconstructed across considerable areas of cliff top. The average rate of erosion at The Grind is estimated at 1.3–6.0 mm/yr on the cliff face and 5 mm/yr on the cliff top, although erosion rates vary in both time and space. Although block movement on the cliff top occurs in most years, erosion of rock by block removal is most active during major storms. Nevertheless, some parts of the cliff top and face remain blackened by lichen and so have experienced little recent erosion over the last 70 years or so. Although erosion occurs at the base of the cliffs, in recent decades it has been concentrated on upper part of the cliff face and top. Cliff-top erosion is most intense where stepped geos act as channels for waves to access the cliff-top. The most active features on the cliff top are the boulder ridges where substantial changes can be traced to storms over the past century. Unlike conventional models of cliff erosion where erosion is concentrated by wave attack at the waterline, wave impacts on this headland may occur on any part of cliff face and top and appear particularly effective on the upper cliff and cliff top platform. [Copyright &y& Elsevier]

• Erosion history reconstructed for craton in southern Finland since 1.5 Ga. • Tiered unconformities and impact structures indicate erosion at <2.5 m/Ma. • Low-temperature thermochronology overestimates former sedimentary cover thickness. • Persistence of Phanerozoic fracture coatings, Palaeogene groundwater and microbiomes. • Cratonic regime has tectonic stability, prolonged shallow burial and ultra-slow erosion. The Earth's cratons are traditionally regarded as tectonically stable cores that were episodically buried by thin sedimentary covers. Cratonic crust in southern Finland holds seven post-1.7 Ga tiered unconformities, with remnants of former sedimentary covers. We use the geometries of the tiered unconformities, along with previously dated impact structures and kimberlite and carbonatite pipes, to reconstruct the erosion and burial history of the craton and to derive estimates of depths of erosion in basement and former sedimentary rocks. The close vertical spacing (<200 m) of the unconformities and the survival of small (D ≤ 5 km) Neoproterozoic and Early Palaeozoic impact structures indicate minor later erosion. Average erosion rates (<2.5 m/Ma) in basement and cover are amongst the lowest reported on Earth. Ultra-slow erosion has allowed the persistence in basement fractures of Phanerozoic fracture coatings and Palaeogene groundwater and microbiomes. Maximum thicknesses of foreland basin sediments in Finland during the Sveconorwegian and Caledonide orogenies are estimated as ~1.0 km and <0.68–1.0 km, respectively. Estimated losses of sedimentary cover derived from apatite fission track thermochronology are higher by factors of at least 2 to 4. A dynamic epeirogenic history of the craton in Finland, with kilometre-scale burial and exhumation, proposed in recent thermochronological models is not supported by other geological proxies. Ultra-slow erosion rates in southern Finland reflect long term tectonic stability and burial of the craton surface for a total of ~1.0 Ga beneath generally thin sedimentary cover. [ABSTRACT FROM AUTHOR]