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1.
Rainfall thresholds for landsliding in the Himalayas of Nepal 总被引：5，自引：0，他引：5
Emmanuel J. Gabet Douglas W. Burbank Jaakko K. Putkonen Beth A. Pratt-Sitaula Tank Ojha 《Geomorphology》2004,63(3-4):131-143
Landsliding of the hillslope regolith is an important source of sediment to the fluvial network in the unglaciated portions of the Himalayas of Nepal. These landslides can produce abrupt increases of up to three orders of magnitude in the fluvial sediment load in less than a day. An analysis of 3 years of daily sediment load and daily rainfall data defines a relationship between monsoonal rainfall and the triggering of landslides in the Annapurna region of Nepal. Two distinct rainfall thresholds, a seasonal accumulation and a daily total, must be overcome before landslides are initiated. To explore the geomorphological controls on these thresholds, we develop a slope stability model, driven by daily rainfall data, which accounts for changes in regolith moisture. The pattern of rainfall thresholds predicted by the model is similar to the field data, including the decrease in the daily rainfall threshold as the seasonal rainfall accumulation increases. Results from the model suggest that, for a given hillslope, regolith thickness determines the seasonal rainfall necessary for failure, whereas slope angle controls the daily rainfall required for failure. 相似文献
2.
An analysis is made of the results from all repeated gravity measurements of the Fennoscandian land uplift gravity line 63°. The line is, thereby, divided into two separate parts: one part west of the land uplift maximum, and the other part east of the land uplift maximum. A statistically significant change of gravity is found both for the western part and the eastern one. Both parts give a relation between gravity change and land uplift of about ?0.22μgal/mm. 相似文献
3.
Jaakko Mkinen 《Journal of Geodynamics》1987,8(2-4)
In order to investigate the variation in gravity caused by the Fennoscandian land uplift, the Nordic countries have established 4 profiles with near-zero gravity differences along the latitudes 65°, 63°, 61° and 56° N. High-precision gravity measurements have been repeatedly made on these lines since 1975, 1966, 1976 and 1977, respectively. The observations have recently been published in one volume. 相似文献
4.
Estimates of regolith degradation in the McMurdo Dry Valleys of Antarctica are currently based on indirect evidence and ancient ashes at or near the soil surface that suggest excellent preservation of surfaces. On the other hand, the existing cosmogenic-nuclide surface exposure ages from many parts of the Dry Valleys are younger than the age of surface deposits inferred from stratigraphic relations. This suggests some combination of surface erosion or past ice cover, both of which would reduce the apparent exposure age. This paper quantifies the regolith degradation and/or past ice cover by measuring 10Be and 26Al from a landslide deposit that contains 11.3 Ma volcanic ash. The surface sample yields an apparent exposure age of only 0.4 Ma. However, measurements of the subsurface nuclide concentrations show that the deposit has not been shielded by ice, and that the age of the ash does not conflict with the apparent exposure age when slow degradation of the deposit (2 m Ma−1) is taken into account. Soil creep, which is a common degradational process in a wide variety of environments, is non-existent at this field site, which likely reflects the persistent lack of bio- and cryoturbation. 相似文献
5.
The treatment of the permanent tidal deformation of the Earth in GPS computation has been an almost unmentioned topic in the GPS literature. However, the ever increasing accuracy and the need to combine the GPS based coordinates with other methods requires a consistent way to handle the tides. Our survey shows that both the ITRF-xx coordinates and the GPS based coordinates are nowadays reduced to a non-tidal crust, conventionally defined using physically meaningless parameters. We propose to use instead the zero-crust concept which corresponds to concepts already accepted in the resolution of IAG in 1983 for gravimetric works. 相似文献
6.
Accuracy of cosmogenic ages for moraines 总被引：1，自引：0，他引：1
Analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38% between the oldest and youngest boulders from each moraine. This range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform. The wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders. A diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders (n = 3-7) will always yield a lower age limit for the moraine. The model indicates that for identical dating accuracy, six to seven boulders are needed from old and tall moraines (40,000-100,000 yr, 50-100 m initial height) but only one to four boulders from small moraines (20,000-100,000 yr, 10-20 m). By following these guidelines the oldest obtained boulder age will be ≥90% of the moraine age (95% probability). This result is only weakly sensitive to a broad range of soil erosion rates. Our analysis of published boulder ages indicates that <3% of all moraine boulders have prior exposure, and 85% of these boulders predate the dated moraine. 相似文献
7.
Mining is one of the key industries in the world and mine water pollution is a serious threat to aquatic ecosystems. Historical monitoring data on the pollution history and impacts in aquatic ecosystems, however, are rarely available, so paleolimnological methods are required to explore the consequences of past pollution. We studied the history of cladoceran community dynamics in Lake Kirkkojärvi, southern Finland, including the periods before, during and after mining. We analyzed the geochemical composition and cladoceran subfossil remains in a 210Pb-dated sediment core to evaluate the magnitude, rate, and direction of cladoceran community changes through time. The cladoceran community was altered significantly by mining activity that occurred during the mid-twentieth century. During more recent times, however, eutrophication effects have overridden the impacts of mining. After mining ceased, the cladoceran community underwent an abrupt regime shift towards taxa that reflect more eutrophic conditions. This change was caused by intensive farming activity and fertilizer use over the past few decades. The recent history of Lake Kirkkojärvi is a textbook example of a regime shift triggered by multiple human-caused stressors. Our findings also highlight the utility of cladocerans as bio-indicators in pollution research and illustrate the sensitivity of aquatic ecosystems to anthropogenic modification. 相似文献
8.
Jaakko Tuominen 《Solar physics》1976,47(2):541-550
Some earlier investigations seem to indicate that sunspots show an average drift in latitude which varies sinusoidally with the period of the double sunspot cycle (about 22 years), while the same investigations do not show similar variability with the period of the single sunspot cycle (about 11 years). Other studies, however, show that the drift of sunspots varies with the period of the single sunspot cycle. There seems to be a discrepancy between the two results. The problem is reinvestigated on the basis of long-lived sunspot groups, but treating the material in a way different from that used before. This procedure, which uses central values of the proper motions of the groups instead of their average values, gives an additional proof of the reality of the 11-year period of the drift. It also seems to produce the 22-year period, but there is such a difference between the variabilities of the drift found on the basis of the two methods that the 22-year cycle of the drift is made doubtful. 相似文献
9.
Oscillator strengths are calculated for 259 lines of Ti i by taking configuration interaction into account in a somewhat simplified treatment. Radial integrals are obtained by an adaptation of the scaled Thomas-Fermi method. The great majority of selected lines originate from slightly perturbed terms. From a satisfactory comparison of our g \({\text{f}}\) -values with recent experimental data and with solar results in the visible region, we have been able to extend the work for some infrared lines. Very few transition probabilities were known for Ti i in that spectral range. On the basis of our oscillator strengths, a mean value logN ti = 4.88 ± 0.12 (in the usual scale), is proposed for the solar photospheric abundance, in agreement with the meteoritic value. 相似文献
10.
Quaternary glaciation of Mount Everest 总被引：1，自引：0，他引：1
Lewis A. Owen Ruth Robinson Douglas I. Benn Robert C. Finkel Nicole K. Davis Chaolu Yi Jaakko Putkonen Dewen Li Andrew S. Murray 《Quaternary Science Reviews》2009,28(15-16):1412-1433
The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24–27 ka (Jilong moraine), 14–17 ka (Rongbuk moraine), 8–2 ka (Samdupo moraines) and ～1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8–7.7 ka) and Samdupo II (～2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation. 相似文献