Surface Lowering Rates Research Articles

Hazard assessment investigations in connection with the formation of a lake on the tongue of Unterer Grindelwaldgletscher, Bernese Alps, Switzerland

Abstract. The surface of Unterer Grindelwaldgletscher glacier tongue has subsided by more than 200 m over the last 150 years. The surface lowering is not uniform over the glacier tongue but depends on the thickness of the uneven debris cover, which led to the formation of a depression on the tongue. A lake can form in this basin, which occurred for the first time in 2005. Such a glacier lake can drain rapidly leading to a so-called outburst flood. The lake basin has been increasing in size at an alarming rate and in 2008, it reached a volume which poses a significant flooding threat to the communities downstream, as was exemplified by an outburst of the lake in May 2008. The future evolution of the lake basin was extrapolated based on surface lowering rates between 2004–2008. An outburst flood model was tuned with the measured hydrograph from 2008 and then was run with the extrapolated lake bathymetries to simulate future lake outbursts and estimate their flood hydrographs. We discuss the rapidly increasing risk for Grindelwald and other communities, as well as the installation of an early warning system and possible prevention measures.

Soil erosion in Slovene Istria

From the end of nineties of the 20th century, intense hydrologic and geomorphologic research is taking place in the Slovene Istria. As a part of this research also studies on soil erosion were undertaken in the period from 2005 to 2008. The field measurements were undertaken on closed 1 m2 large erosion plots under three different land uses (on bare soils in an olive grove, on an overgrown meadow, in a forest), placed south of the Marezige village in the Rokava River basin. We show weekly measurements of surface erosion (interrill erosion) for the period of 13 months (the end of March 2005 - the end of April 2006), as well as monthly and seasonal averages together with selected linear statistical correlations between soil erosion and weather parameters. From May 2005 to April 2006 the interrill erosion on bare soils in an olive grove with an inclination of 5.5° amounted to 9013 g/m2 (90 t/ha) that corresponds to surface lowering rate of 8.5 mm/yr; on an overgrown meadow with an inclination of 9.4° it amounted to 168 g/m2 (1,68 t/ha) that corresponds to surface lowering rate of 0.16 mm/ /yr; and in a forest with an inclination of 7.8° it amounted to 391 g/m2 (3,91 t/ha) and in a forest with an inclination of 21.4° it amounted to 415 g/m2 (4,15 t/ha), respectively, that corresponds to surface lowering rate of 0.4 mm/yr.

Morphological and ice-dynamical changes on the Tasman Glacier, New Zealand, 1990–2007

This paper presents data concerning recent (1990–2007) surface morphological and ice-dynamical changes on the Tasman Glacier, New Zealand. We use remote-sensing data to derive rates of lake growth, glacier velocities and rates of glacier surface lowering. Between 1990 and 2007, the glacier terminus receded ~ 3.5 km and a large ice-contact proglacial lake developed behind the outwash head. By 2007 the lake area was ~ 6 km 2 and had replaced the majority of the lowermost 4 km of the glacier tongue. There is evidence that lake growth is proceeding at increasing rates — the lake area doubled between 2000 and 2007 alone. Measured horizontal glacier velocities decline from 150 m a − 1 in the upper glacier catchment to almost zero at the glacier terminus and there is a consequent down-glacier increase in surface debris cover. Surface debris mapping shows that a large catastrophic rockfall onto the glacier surface in 1991 is still evident as a series of arcuate debris ridges below the Hochstetter icefall. Calculated glacier surface lowering is most clearly pronounced around the terminal area of the glacier tongue, with down-wasting rates of 4.2 ± 1.4 m a − 1 in areas adjacent to the lateral moraine ridges outside of the current lake extent. Surface lowering rates of approximately 1.9 ± 1.4 m a − 1 are common in the upper areas of the glacier. Calculations of future lake expansion are dependent on accurate bathymetric and bed topography surveys, but published data indicate that a further 8–10 km of the glacier is susceptible to calving and further lake development in the future.

Holocene microweathering rates and processes on ice-eroded bedrock, Røldal area, Hardangervidda, southern Norway

Abstract Post-glacial weathering of ice-eroded metamorphic bedrock was investigated in the Røldal area (60°N) of the Hardangervidda Plateau in southern Norway. Quartz veins were used as reference surfaces to determine a mean post-glacial surface lowering rate of 0.55 mm ka −1 . Chemical characteristics of late-season runoff were determined for one catchment (Snøskar) and a chemical erosion rate of 4.9 t km −2 a −1 was obtained. A mean in situ fracture enlargement due to microweathering of 0.12 mm ka −1 was also determined. These rates are low, although comparable with similar environments in cold regions, and suggest that microweathering has had relatively little impact on Holocene landscape evolution. Weathering rind thickness was found to be less on fracture walls than on exposed bedrock surfaces, suggesting fractures have not played a significant role in microweathering. Observations of weathering morphology reveal a range of forms including shallow spalling, tafoni and pseudokarren, indicating locally intense weathering activity. Analysis of interrelationships between multiple weathering indices points to the importance of bedrock microweathering as a precursor to macro-breakdown and landform evolution. The research reasserts the importance of chemical activity in cold environments and the importance of moisture supply for effective microweathering.

Decadal scale micro erosion rates on shore platforms

Knowledge of the long-term rates of erosion of shore platforms are needed to assist modeling platform development, understand rates and modes of development and decipher issues of inheritance from former sea level. Few studies report rates from more than 2 years of monitoring. We report decadal scale erosion rates using both a micro-erosion meter and a traversing micro-erosion meter with measurements from 30 years and 10 years, respectively. Gross mean surface lowering rates measured over 10 years with a traversing micro-erosion meter were 0.901 (S.E. = 0.116) mm/yr compared with 1.130 (S.E. = 0.217) mm/yr over two years. Over thirty years (1973–2003) 12 micro-erosion meter sites provide a mean surface lowering rate of 1.09 (S.E. = 0.126) mm/yr compared to 1.43 (S.E. 0.128) mm/yr calculated over twenty years (1973–1993) from 15 bolt sites and 1.53 (S.D. = 1.45) mm/yr from 31 bolt sites. Rates calculated over longer time periods are reduced compared to short-term rates as a result of faster eroding bolt sites being removed from the data set. Comparison of means between short and long time periods for existing bolts show no significant difference. That is, short-term measurements over two years are representative of decadal scale erosion rates. In fact decadal scale rates may under represent rates of platform development because of the loss of faster eroding bolt sites. The loss of such bolts means that obtaining long-term erosion rates is problematic. Future modeling of shore platform development can use MEM rates with more certainty, but we recommend using higher rates from shorter term studies, unless longer records are complete.

Rock control on microweathering of bedrock surfaces in a periglacial environment

Microweathering of ice-smoothed bedrock surfaces was investigated in the Røldal area of Hardanger Plateau (60°), southern Norway. Postglacial rates of weathering were determined from surface lowering using quartz veins as reference surfaces. Weathering processes are inferred from assessment of weathering rind formation, surface hardness, and the preservation of small-scale glacial erosional features. Surface lowering rates for a range of metamorphic rocks vary from 0.05 to 2.20 mm ka − 1 and are broadly comparable with those obtained from crystalline rocks in other periglacial environments. The mean rate of surface lowering at 0.55 mm ka − 1 is low and demonstrates the relatively small impact of microweathering on postglacial landscape evolution. Variations in bedrock microweathering can be explained by lithological variation. Amphibolite and mica-rich bedrock surfaces experience greater denudation and weakening, least weathering rind formation, and abundant preservation of glacial striae, despite greater surface lowering. Conversely, quartz-rich bedrock surfaces are most resistant to denudation and weakening, but have greater weathering rind formation and fewer preserved striae. Postglacial microweathering is achieved primarily through granular disintegration involving detachment and removal of mineral grains and weakening from increased porosity. Granular decomposition is manifest in the formation of weathering rinds. Analysis of interactions between weathering indices indicates that rind accumulation is limited by microerosion. A conceptual model is proposed that illustrates the temporal interrelationships between in situ and erosional facets of microweathering in two contrasting mineral assemblages. The model proposes that cyclic processes of in situ disintegration, decomposition, and erosion are at work. The relative balance between these processes varies with lithology so that in more resistant quartz-rich rocks the net effect is minimal surface lowering and accumulation of weathering rind. In weaker, amphibolitic and micaceous rocks, the net effect is greater surface lowering and minimal accumulation of weathering rind. The results of the research demonstrate the important influence of rock properties, notably mineral composition, in postglacial microweathering of crystalline bedrock in a periglacial environment.

Surging, accelerating surface lowering and volume reduction of the Malaspina Glacier system, Alaska, USA, and Yukon, Canada, from 1972 to 2006

AbstractNear-concurrent surges and multi-decadal surface-elevation changes on the Malaspina Glacier system Alaska, USA, and Yukon, Canada, were investigated using digital elevation models and laser altimetry from airborne and space-borne sensors. Surface-elevation changes on Seward Lobe in two time periods support a hypothesis of moraine folding by a mechanism of sequential surges alternating from southeast to south-southwest. The near-concurrent surges of Agassiz, Lower Seward and Marvine glaciers support a hypothesis of englacial water storage being a critical factor of surging. Acceleration of area-average surface lowering on the piedmont glaciers occurred, from 1.5 ± 0.1 m a−1 between 1972 and 1999 to 2.3 ± 0.3 m a−1 between 1999 and 2002. On the western half of Upper Seward Glacier, above 1600 m, acceleration of surface lowering occurred from 2000 to 2003 relative to that from 1976 to 2000, indicating an effect from the surge of Lower Seward Glacier. From 2003 to 2006, the rate of surface lowering on Upper Seward Glacier has moderated back to the pre-2000 rate, indicating a recovery of surface elevation following the surge. From 1972 to 2002, the Malaspina Glacier system lost 156 ± 19 km3 (ice equivalent) on an area of 3661 km2.

Rates of Holocene chemical weathering, `Little Ice Age' glacial erosion and implications for Schmidt-hammer dating at a glacier—foreland boundary, Fåbergstølsbreen, southern Norway

Average rates of Holocene chemical weathering and `Little Ice Age' glacial erosion of bedrock are estimated across the glacier—foreland boundary of an outlet glacier of the Jostedalsbreen ice-cap, southern Norway. Estimates are derived from two types of evidence: (1) the heights of quartz veins above adjacent surfaces of granitic or granodioritic gneiss; and (2) Schmidt-hammer R-values of rock hardness. Average and maximum rates of surface lowering of gneiss surfaces by chemical weathering are 1.63 and 3.61 mm/ka, respectively, whereas many quartz veins exhibit negligible weathering after c. 9700 years. `Little Ice Age' glacial erosion rates are at least two orders of magnitude greater than the chemical weathering rates, except in a narrow marginal zone inside, but close to, the `Little Ice Age' limit, where patches of weathered surface survive. Bedrock surfaces outside and well inside the `Little Ice Age' glacier—foreland boundary are shown to have potential for improved calibrated-age dating using R-values, compared with moraine surfaces.

Surface lowering rates of uplifted limestone terraces estimated from the height of pedestals on a subtropical island of Japan

AbstractIn Kikai‐jima, south‐western Japan, many pedestal rocks have developed on the surface of Holocene raised coral‐reef terraces with known dates of emergence. Pedestals are formed just under boulders, which are considered to have been transported by tsunami and settled on a reef flat before emergence. On the assumption that boulders protect the underlying limestone terrace from rainfall solution, the rate of surface lowering of these limestone terraces was evaluated from the height of pedestals and the period of their formation. The result showed that the mean lowering rate over 6000 years is 205 mm/ky. Copyright © 2007 John Wiley & Sons, Ltd.

The World’s Oldest Caves: - How -Did They Survive and What Can They Tell Us?

Parts of an open cave system we can walk around in today are more than three hundred million years old. Common sense tells even enthusiasts like me that open caves this old should not still exist, but they do! Their survival can be partly explained by extremely slow rates of surface lowering, but this is not sufficient by itself. Isolation by burial and relative vertical displacement by faults are probably also required. Now one very old set of caves have been found, are there more of them? What can they tell us?

Bedrock slope evolution in saltrock terrain

Saltrock is a highly soluble terrain-forming material and, over short periods of time under predominantly solutional erosion processes, shows readily measurable change. It provides an analogue for landform evolution on less rapidly soluble materials such as limestone and gypsum. Saltrock erosion in a Mediterranean environment is observed with erosion pins on both solid outcrop and rockfall debris. Erosion of the salt terrains is very closely related to rainfall events. Surface lowering rates of up to 20 mm per 100 mm rainfall are observed, representing an annualised rate of ca 100 mm a−1 (= 10 m per century or 100 m per millennium). Clear relationships, which are described by bivariate polynomial equations, exist between slope angle and erosion rate. Slope evolution is then modelled with these equations, to reveal good correspondence with the small-scale landforms present at the field sites.

Regolith thickness instability and the formation of tors in arid environments

We present model results suggesting that a physical erosion–bedrock weathering feedback is responsible for the development of isolated bedrock knobs (tors/inselbergs) that often punctuate otherwise smooth pediments of homogeneous basement lithology. Tors and larger, more heavily jointed and morphologically complex exposures, inselbergs, may arise as a consequence of fluctuations in rainfall and sediment transport conditions combined with a bedrock weathering mechanism that depends on regolith thickness. Hydrogeochemical considerations and field observations in arid, granitic environments suggest that the relationship between weathering rate and regolith thickness exhibits a maximum for a finite thickness of cover. We have encapsulated this simple erosion‐weathering feedback in a numerical model simulating arid/semiarid landscape evolution that produces low‐sloping pediments punctuated by tors. Tors form during periods of higher effective moisture, resulting in local base level incision and regolith thinning on pediments, invoking a transition in which mantled surfaces lower at rates exceeding the bare bedrock weathering rate. This condition favors the emergence and growth of tors in areas covered by regolith thickness less than a threshold value. Subsequent shifts in climate or local base level that restore sediment surface lowering rates less than the bare bedrock weathering rate will lead to a progressive decrease in tor height and, ultimately, their disappearance. Thus, according to this model, tors in arid environments represent possibly transient features related to fluctuations in climate or local transport conditions rather than palimpsests of an ancient landscape derived from differential subsurface weathering followed by regolith stripping.

Estimates of Soil Erosion from Perched Cemeteries, Sampson County, North Carolina

The Coastal Plain of the United States has not been recognized traditionally as a region experiencing significant soil erosion because of its low relief and permeable soils. Measurements of soil profile truncation in cemeteries were used to estimate rates of surface lowering and soil erosion in Sampson County, on the Coastal Plain of North Carolina. Measurements of the depth to the top of the argillic horizon (DTA) in relatively undisturbed profiles in small, perched cemeteries (ranging in age from 99—180 yr) were compared with adjacent cultivated fields. The mean truncation of soils from ten study sites was 25.8 cm, with the mean surface lowering of 2.0 cm. Correcting for compaction, this translates to a mean soil loss estimate of 24.4&8211;27.4 Mg/ha/yr.

Isotopic insights into smoothening of abandoned fan surfaces, Southern California

Cosmogenic nuclide concentrations measured on abandoned fan surfaces along the Mojave section of the San Andreas Fault suggest that sediment is generated, transported, and removed from the fans on the order of 30–40 kyr. We measured in situ produced cosmogenic 10Be, and in some cases 26Al, in boulders ( n = 15), surface sediment ( n = 15), and one depth profile ( n = 9). Nuclide concentrations in surface sediments and boulders underestimate fan ages, suggesting that 10Be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages. Field observations, grain-size distribution, and cosmogenic nuclide data suggest that over time, boulders weather into grus and the bar sediments diffuse into the adjacent swales. As fans grow older the relief between bars and swales decreases, the sediment transport rate from bars to swales decreases, and the surface processes that erode the fan become uniform over the entire fan surface. The nuclide data therefore suggest that, over time, the difference in 10Be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized, resulting in a common surface lowering rate and common 10Be concentrations across the fan. During this phase, the entire fan is lowered homogeneously at a rate of 10–15 mm kyr −1.

Rapid Holocene chemical weathering on a calcitic lake shoreline in an alpine periglacial environment: Attgløyma, Sognefjell, southern Norway

AbstractA small lake (Attgløyma) at an altitude of about 1220 m in the low‐alpine zone, southern Norway, has a shore platform in calcitic and quartzitic muscovite‐chlorite schists. The platform has recently been exposed by a fall in lake level due to upstream dam construction and exhibits micro‐landforms ranging from pits and grooves to upstanding crenulate ridges produced by differential chemical weathering under relatively constant conditions over the last ca. 10 000 years. The maximum surface lowering rate of the calcitic layers estimated from differential weathering is 35 mm ka−1, which is about an order of magnitude greater than most previous estimates from alpine and polar periglacial environments. Average bedrock surface lowering across the whole platform reached a maximum of 15.5 ± 2.2 mm ka−1 in a vertical zone corresponding with the former lake level, declining to negligible values around 0.7 m below lake level. Differential weathering and bedrock surface lowering were also negligible immediately above lake level. Correspondence of maximum surface lowering rates with the former lake level and a shoreline notch at the back of a platform suggest that the effects of solutional weathering of the calcite have been enhanced by water movement generated by small lake‐surface waves. Copyright © 2006 John Wiley & Sons, Ltd.

Landscape development in an hyperarid sandstone environment along the margins of the Dead Sea fault: Implications from dated rock falls

In this study, we explored the spatial and temporal relations between boulders and their original in-situ locations on sandstone bedrock cliffs. Thiswas accomplished bycombining field observations withdating methods using cosmogenicisotopes ( 10 Be and 14 C) and optically stimulated luminescence (OSL). Our conclusions bear both on the landscape evolution and cliff retreat process in the hyperarid region of Timna and on the methodology of estimating exposure ages using cosmogenic isotopes. We recognize three discrete rock fall events, at 31 ka, 15 ka, and 4 ka. In this hyperarid region, the most plausible triggering mechanism for rock fall events is strong ground acceleration caused by earthquakes generated by the nearby Dead Sea fault (DSF). Our record, however, under represents the regional earthquake record implying that ongoing development of detachment cracks prior to the triggering event might be slower than the earthquake cycle. Cliff retreat rates calculated using the timing of rock fall events and estimated thickness of rock removed in each event range between 0.14 m ky � 1 and 2 m ky � 1 . When only full cycles are considered, we derive a more realistic range of 0.4 m ky � 1 to 0.7 mk y � 1 . These rates are an order of magnitude faster than the calculated rate of surface lowering in the area. We conclude that sandstone cliffs at Timna retreat through episodic rock fall events that preserve the sharp, imposing, landscape characteristic to this region and that ongoing weathering of the cliff faces is minor. A 10%–20% difference in the 10 Be concentrations in samples from matching boulder and cliff faces that have identical exposure histories and are located only a few meters apart indicates that cosmogenic nuclide production rates are sensitive to

Characterizing Land Surface Erosion from Cesium‐137 Profiles in Lake and Reservoir Sediments

Recognition of the threat to the sustainable use of the earth's resources posed by soil erosion and associated off-site sedimentation has generated an increasing need for reliable information on global rates of soil loss. Existing methods of assessing rates of soil loss across large areas possess many limitations and there is a need to explore alternative approaches to characterizing land surface erosion at the regional and global scale. The downcore profiles of 137Cs activity available for numerous lakes and reservoirs located in different areas of the world can be used to provide information on land surface erosion within the upstream catchments. The rate of decline of 137Cs activity toward the surface of the sediment deposited in a lake or reservoir can be used to estimate the rate of surface lowering associated with eroding areas within the upstream catchment, and the concentration of 137Cs in recently deposited sediment provides a basis for estimating the relative importance of surface and channel, gully, and/or subsurface erosion as a source of the deposited sediment. The approach has been tested using 137Cs data from several lakes and reservoirs in southern England and China, spanning a wide range of specific suspended sediment yield. The results obtained are consistent with other independent evidence of erosion rates and sediment sources within the lake and reservoir catchments and confirm the validity of the overall approach. The approach appears to offer valuable potential for characterizing land surface erosion, particularly in terms of its ability to provide information on the rate of surface lowering associated with the eroding areas, rather than an average rate of lowering for the entire catchment surface.

Tortoises and hares: dissolution, erosion and isostasy in landscape evolution

AbstractDenudation mechanisms differ fundamentally between limestone and silicate rock types, which are subject to very different rate thresholds and enhancers/inhibitors. Silicates are removed largely by erosion, the mechanical entrainment and transport of particles. This is a relatively high energy, and highly episodic, process which occurs only when a minimum threshold flow velocity is exceeded; it is inhibited by vegetation cover and favoured by strongly seasonal runoff. Limestone is removed largely by chemical dissolution at a rate directly proportional to runoff. Dissolution is a relatively low energy process that can occur at any flow velocity or in static water; in general it is enhanced by vegetation cover and non‐seasonality of runoff. These contrasting factors in the denudation of silicates versus limestone can produce strikingly uneven rates of surface lowering across a landscape, sometimes akin to the well known ‘tortoise and hare race’, where the slow and steady denudation of limestones may in the long term exceed the sometimes rapid, but often localized and episodic, erosion of silicates. Prolonged exposure of limestone to a humid temperate climate in a tectonically stable environment produces low‐relief corrosion plains in which limestone uplands are anomalous and, in most instances, due to recent unroofing from beneath a siliciclastic cover. In a highly seasonal or semi‐arid climate almost the exact inverse may develop, with ‘flashy’ runoff and sparse vegetation favouring erosion rather than dissolution. Even under a constant humid climate progressive unroofing of a thick limestone unit within folded siliciclastics may lead to a topographic inversion over time, with the limestone outcrop always forming a topographic low flanked by siliciclastic uplands. Valleys will be initiated on anticlinal crests, where the limestone is first unroofed, but progressive lowering of the limestone causes these valleys to migrate to their final position in the synclinal troughs. In humid climates isostatic compensation in response to slow, but continuous, denudation of extensive limestone outcrops may be a significant factor in the development of relief on adjacent, more slowly eroding, silicate outcrops. Copyright © 2004 John Wiley & Sons, Ltd.

Impact of an extreme melt event on the runoff and hydrology of a high Arctic glacier

AbstractOn 28–30 July 2000, an extreme melt event was observed at John Evans Glacier (JEG), Ellesmere Island (79° 40′N, 74° 00′W). Hourly melt rates during this event fell in the upper 4% of the distribution of melt rates observed at the site during the period 1996–2000. Synoptic conditions during the event resulted in strong east‐to‐west flow over the northern sector of the Greenland Ice Sheet, with descending flow on the northwest side reaching Ellesmere Island. On JEG, wind speeds during the event averaged 8·1 m s−1 at 1183 m a.s.l., with hourly mean wind speeds peaking at 11·6 m s−1. Air temperatures reached 8°C, and rates of surface lowering measured by an ultrasonic depth gauge averaged 56 mm day−1. Calculations with an energy balance model suggest that increased turbulent fluxes contributed to melt enhancement at all elevations on the glacier, while snow albedo feedback resulted in increased melting due to net radiation at higher elevations. The event was responsible for 30% of total summer melt at 1183 m a.s.l. and 15% at 850 m a.s.l. Conditions similar to those during the event occurred on only 0·1% of days in the period 1948–2000, but 61% of events occurred in the summer months and there was an apparent clustering of events in the 1950s and 1980s. Such events have the potential to impact significantly on runoff, mass balance and drainage system development at high Arctic glaciers, and changes in their incidence could play a role in determining how high Arctic glaciers respond to climate change and variability. Copyright © 2003 John Wiley & Sons, Ltd.

The fluvial morphodynamics of two small permafrost drainage basins, Richardson Mountains, Northwestern Canada

AbstractBased on hydrological fieldwork in the tundra of northwestern Canada during the springs of 1986, 1990, 1992, and 1994 and the summers of 1998, 1999, and 2000 the paper deals with the fluvial processes induced by spring snowmelt and by summer rainfall in two small stream valleys. At the end of winter the floors of these flat‐bottomed valleys are covered by icings (aufeis) over most of their length. The biggest quantity of meltwater runoff passes in an ice channel on top of the icing, with flow velocities up to 4.8 m/s. The main solid‐sediment transport takes place through the short runoff interval, when the stream channel has entrenched the aufeis in some places. The calculated suspended load transport during snowmelt flood varied from 62–313 t/km2 in different years. In summer, suspended‐sediment transport varies between 0.2–1.4 t/km2. There are no data about the frequency of exceptionally strong precipitation events, similar to those that occurred during the 1999 summer in the Douglas Creek basin that led to a suspended load transport of 153 t/km2 and a bedload transport of 444 t/km2 in about 12 days. The average annual suspended‐sediment yield for Andy Creek is 71 t/km2/yr, and 328 t/km2/yr for Douglas Creek. The average annual solutes yield for Andy Creek is 19 t/km2/yr, and 52 t/km2/yr for Douglas Creek. If one includes the hardly‐recordable bedload transport, the total equivalent surface lowering rate by fluvial solids transport is about 350 mm/1000yr for the Andy Creek basin and 850 mm/1000yr for the Douglas Creek basin. Copyright © 2002 John Wiley & Sons, Ltd.