Norikazu Matsuoka

Solifluction rates, processes and landforms: a global review

Abstract Field data on the rates of solifluction and associated parameters are compiled from the literature, in an attempt to evaluate factors controlling the spatial variability in solifluction processes and landforms, with special attention on the climate–solifluction relationship. The analyzed data originate from 46 sites over a wide range of periglacial environments, from Antarctic nunataks to tropical high mountains. Solifluction, broadly defined as slow mass wasting resulting from freeze–thaw action in fine-textured soils, involves several components: needle ice creep and diurnal frost creep originating from diurnal freeze–thaw action; annual frost creep, gelifluction and plug-like flow originating from annual freeze–thaw action; and retrograde movement caused by soil cohesion. The depth and thickness of ice lenses and freeze–thaw frequency are the major controls on the spatial variation in solifluction processes. Near the warm margin of the solifluction-affected environment, diurnal freeze–thaw action induces shallow but relatively rapid movement of a superficial layer 5–10 cm thick on average, often creating the thin stone-banked lobes typically seen on tropical high mountains. In addition to diurnal movement, annual frost creep and gelifluction may occur on slopes with soil climates of seasonal frost to warm permafrost, dislocating a soil layer shallower than 60 cm at a rate of centimeters per year and eventually producing medium-size solifluction lobes. In High-Arctic cold permafrost regions, two-sided freezing can induce plug-like flow of a soil mass 60 cm or thicker. The correlation between process and landform suggests that the riser height of lobes is indicative of the maximum depth of movement and prevailing freeze–thaw type. Climate change may result in new different ground freezing conditions, thereby influencing the surface velocity and maximum depth of soil movement. Soil moisture and topography also control solifluction. High moisture availability in the seasonal freezing period enhances diurnal freeze–thaw action and subsequent seasonal frost heaving. The latter contributes to raising the moisture content of the thawed layer and promotes gelifluction during the thawing period. The slope angle defines the upper limit of the surface velocity of solifluction. A diagram correlating the potential frost creep with the actual surface velocity permits an inter-site comparison of the relative magnitude of solifluction components. Physically based modelling of periglacial slope evolution requires synthetic and more detailed field monitoring and laboratory simulations of solifluction processes.

Rockfall activity from an alpine cliff during thawing periods

Abstract Rockfall activity during thawing periods was investigated by collecting rockfall debris fallen on the snow-covered talus slope in a cirque in the Japanese Alps. Near-surface rock temperature was also monitored on the cirque wall. Maximum rockfall activity occurs on average about 10 days after the meltout of the cirque wall. The intensive activity is rarely associated with precipitation events or diurnal frost cycles on the rockface. A thermal conduction model suggests that rockfalls at this site occur most frequently when the seasonal thawing front penetrates to a depth of about 1 m in the bedrock. While the freeze–thaw penetration controls the maximum dimensions of detachable rock mass, joint spacing on the rockface affects the size distribution of rockfall debris. Boulder falls resulting from seasonal frost weathering are considered to be the most important process responsible for the contemporary modification of the cirque wall. The rockfall volume during a thawing period is usually 1–3 m3, which is equivalent to the rate of cirque wall retreat of the order of 0.01 mm year−1. However, big boulder falls that occur once per decade can increase the retreat rate significantly.

Mechanisms of rock breakdown by frost action: an experimental approach.

Abstract Freezing behavior and frost shattering of rocks were studied in the laboratory. Rates of frost shattering were determined for 47 different samples of saturated rocks partially immersed in water by a decreasing rate of the longitudinal wave velocity during freeze-thaw cycles. The ratio of surface area per unit volume to tensile strength gives a good estimation of the frost shattering rate. This indicates that water migration caused by adsorptive suction participates in the frost shattering, as well as the 9% volumetric expansion. Frost shattering occurred in porous rocks despite the lower saturation level than the theoretical value derived from the volumetric expansion theory. Furthermore, the open system was much more effective in frost shattering than the closed system was. Such moisture effects also demonstrate the large role of water migration in frost shattering. The linear strain of some saturated rocks during a freeze-thaw cycle was measured with foil strain gauges. Immersion in water increased the freezing expansion of tuffs, although it affected the strain of a shale and an andesite only little. Low cooling rates resulted in small freezing expansion of rocks placed under the closed system because of creep of pore ice. These results suggest that the freezing expansion of a rock consists of three components: two positive strains due to the 9% volumetric expansion of water, and water migration controlled by adsorptive suction, and a negative strain due to creep of ice. The frost shattering of the tuffs would be primarily controlled by the water migration, and that of the shale and andesite is probably caused by the volumetric expansion. The relative contribution of the two processes on frost shattering may depend on the surface area per unit volume of the rocks.

Rock weathering processes and landform development in the Sør Rondane Mountains, Antarctica

Abstract Field observations of weathering processes and the related landforms, combined with laboratory analyses of weathering products, permit a synthetic evaluation of Late Cenozoic weathering environments in the Sor Rondane Mountains, Antarctica, an arid upland characterized by low temperatures and strong winds. Rates and character of weathering depend mainly on moisture availability and the bedrock geology. Under the humid weathering regime that occurs only locally around the margin of the present sheet, frequent diurnal freeze-thaw cycles in summer cause relatively rapid rock fragmentation. Most of the mountains are situated in the arid weathering regime, under which rock breakdown is very slow unless the rock contains plenty of salts. Salt weathering becomes more intensive and extensive with exposure age, as a result of salt accumulation in rock, eventually producing soils as small as fine-silt size. Lack of clay mineralization even in weathered rocks having been exposed above the ice sheet prior to 4 Ma ago indicates that hydrolysis or carbonation of rock minerals has been insignificant during the past 4 Ma. The final products of weathering are due mainly to salt action and reflect the parent lithology. Resistant fine-grained granite forms strongly oxidized tors carved with tafoni, or fields of mushroom-like boulders overlying the fractured bedrock. Less resistant rocks, like biotite gneiss and amphibolite, produce stone pavements underlain by saline, silty soils up to 30–40 cm thick, the thickness of which corresponds to the maximum thaw depth.

Differential frost heave and sorted patterned ground: field measurements and a laboratory experiment

Abstract Small-scale sorted stripes and circles dominate over the alpine regions in the Upper Engadin, Swiss Alps. Most of these features are spaced at less than 30 cm intervals by coarse margins shallower than 5 cm. Monitoring of sorted stripes indicates that shallow diurnal freezing often induces differences in amount and timing of frost heave by needle ice growth between fine and coarse stripes, while deeper diurnal freezing and seasonal freezing rarely differentiate heave amounts of the two materials. A laboratory simulation is designed to explore the contribution of differential frost heave to the sorting process at the monitoring site. The device consists of a fine part (loam) and a coarse part (a granule layer mounted on loam). Freeze–thaw tests with a granule mantle of 0.5, 2.5 and 5 cm thick demonstrate that the heave amount on the coarse part is greatly reduced by the 5-cm-thick mantle, and that the coarse part always heaves later but subsides earlier than the fine. As a result of this time lag in frost heaving, lateral soil movement towards the coarse part is generated within the surficial soil. Differential heave associated with diurnal freeze–thaw cycles is capable of sorting of the top 5 cm of soil.

Soil moisture variability in relation to diurnal frost heaving on Japanese high mountain slopes

Frost heave, ground temperature and moisture were concurrently monitored on two alpine slopes with thin debris mantles. Electrical sensors connected to data loggers permitted automated monitoring of the three variables. Diurnal frost heave of up to 3 cm frequently took place during spring and autumn. Soil moisture contents are regarded as the primary control on the amount of frost heave, while the intensity of freezing is secondary. Heave was usually greatest just after a major rainstorm that produced high moisture contents in the near-surface soil, and decreased with soil desiccation. Rainstorms often interrupted the desiccation process and reactivated frost heaving. Despite reaching a depth of 1 m or more, seasonal frost penetration caused only small amounts to heave, because the lower part of the seasonally frozen layer was not frost-susceptible. These observations imply that the thin debris mantle and periodic precipitation during periods of freeze-thaw combine to result in the predominance of shallow frost creep, which is typical of soil movements in Japanese high mountains.

FIELD EXPERIMENTS ON PHYSICAL WEATHERING AND WIND EROSION IN AN ANTARCTIC COLD DESERT

Field experiments were carried out over a five year period with the aim of understanding contemporary weathering and erosional environments in the Sor Rondane Mountains, an Antarctic cold desert region. These include observations of (1) scaling from rockwalls, (2) disintegration of tuff blocks with or without saline solutions, and (3) abrasion of artificial walls by wind. Monitoring was also made of rock surface temperature and wind speed. Despite frequent temperature oscillations across 0°C, rock scaling due to frost action was generally very slow because of low moisture content in the rockwalls. Exposure to the cold, dry climate led to the rapid disintegration of porous tuff blocks including soluble salts like halite and thenardite. This indicates that rates of weathering are increased greatly with the accumulation of such salts in the bedrock. Although gypsum did not cause any visible damage over four years, its widespread occurrence in heavily damaged rocks demonstrates that increasing gypsum contents may also intensify rock breakdown. The snow-laden katabatic wind resulted in rapid wearing of the windward face of an asbestos board with the peak erosion at 30–40 cm above the ground. Nonetheless, the landforms expected from the unidirectional wind characteristics are by no means common features because of lack of abrasive materials, such as snow and sand particles. These experiments suggest that frost weathering and wind erosion are only locally effective where plenty of moisture or an abrasive material is available, whilst salt weathering and removal of the waste by wind play a major role in constructing erosional landforms over the mountains.

MUDBOIL AND ICE‐WEDGE DYNAMICS INVESTIGATED BY ELECTRICAL RESISTIVITY TOMOGRAPHY, GROUND TEMPERATURES AND SURFACE MOVEMENTS IN SVALBARD

Abstract Arctic tundra surfaces are dominated by a variety of patterned ground forms. Whereas a large number of studies have described morphology, structure and processes of patterned ground, few have monitored detailed patterned ground dynamics and subsurface environments continuously. We applied electrical resistivity tomography (ERT) to understand near‐surface conditions of two types of patterned ground, ice‐wedge polygons and mudboils in Svalbard, where periglacial processes associated with permafrost are intensively monitored. Automated monitoring shows surface movement characterized by annual cycles of frost heave and thaw settlement, the amounts and rates of which are influenced by the intensity of ice segregation. A time series of ERT shows (1) a distinct resistivity boundary delimiting the active‐layer depth, (2) seasonal variation in resistivity controlled by thermo‐hydrological dynamics and (3) spatial variation in resistivity reflecting desiccation in summer and intensive ice segregation in winter. These results demonstrate ERT as a useful complementary technique for monitoring active‐layer depths and near‐surface hydrological conditions at periglacial patterned ground sites, where automated soil thermal and moisture measurements are limited.

Frost sorting on slopes by needle ice: a laboratory simulation on the effect of slope gradient

Following a previous attempt to reproduce miniature sorted patterns on a level surface, we report the results of a full-scale laboratory simulation on frost sorting produced by needle ice activity on inclined surfaces. Four models, with different slope gradients (5°, 7°, 9°, 11°), were designed. Stones 6 mm in diameter placed in a grid covered 20% of the surface of frost-susceptible water-saturated soil. These models were subjected to 20–40 freeze-thaw cycles between 10°C and −5°C in 12 hours. The evolution of surface patterns was visually traced by photogrammetry. Needle ice growth and collapse induced downslope movement and concentrations of stones. A model produced incipient sorted circles on a 5° slope, whereas it resulted in three distinct sorted stripes on a 7° slope. The average diameter or spacing of these forms is 9.7–19.4 cm, comparable to those in the field dominated by diurnal freeze-thaw cycles. Surface parallel displacements of stone markers were traced with motion analysis software. The observed downslope stone displacements agree with those expected assuming that surface soil and stones move by repeated heaving perpendicular to the surface and vertical settlement due to gravity, although the growth of curved needle adds complexity to the overall displacements.