Total Landslide Volume Research Articles

Rainfall conditions, typhoon frequency, and contemporary landslide erosion in Japan

Dealing with predicted increases in extreme weather conditions due to climate change requires robust knowledge about controls on rainfall-triggered landslides. We explore relationships between rainfall and landslide size throughout the Japanese archipelago. We test whether the total volume of landslides can be predicted directly from rainfall totals, intensity, and duration using a nationwide inventory of 4744 rainfall-triggered landslides recorded from A.D. 2001 to 2011. We find that larger landslides were more abundant at the expense of smaller ones when total, maximum, and mean rainfall intensity exceeded ∼250 mm, ∼35 mm/h, and ∼4 mm/h, respectively. Frequency distributions of these rainfall parameters are peaked and heavily skewed. Yet neither the most frequent nor the most extreme values of these rainfall metrics coincide consistently with the maximum landslide volumes. A striking decrease of landslide volumes at both mean and maximum rainfall intensity, as well as duration, points to an exhaustion in hillslope geomorphic response regardless of sample size, landslide type, mobilized volume, dominant lithology, or reporting bias. Our results underscore substantial offsets between the peaks of rainfall metrics and maximum associated landslide volumes, thus complicating straightforward estimates of geomorphic work from metrics of rainstorm magnitude or frequency. Only the rainfall total appears to be a suitable monotonic predictor of landslide volumes mobilized during typhoons and frontal storms.

Morphogenic uncertainties of the 2008 Wenchuan Earthquake: Generating or reducing?

Landscape evolution in active orogen region is inevitably affected by landslides associated with strong earthquakes, rain or storm. However, quantitative studies of the orogenic or eroded volumes are rarely demonstrated. The 2008 Wenchuan Earthquake triggered serious landsliding, consequently, a large amount of landslide material. However, the landslide volume is estimated mainly on the landslides areas interpreted in their semi-automated landslide mapping algorithm. However, the total volume of landslides triggered by the Wenchuan Earthquake amounts to 5–10 times bigger than the expected upper bound according to the empirical correlation between “total landslide volume” and “moment magnitude”. Here we show that the total landslide volume estimation has large uncertainties to be used to determine whether the Wenchuan Earthquake generates or reduces relief. Thus, the widely held view that large dip-slip and oblique-slip earthquakes build mountainous topography may still be applicable to the Wenchuan Earthquake in Longmen Shan area. To challenge this view, simple landslide volume and co-seismic uplift comparison is not enough, i.e., more data are needed.

Average landslide erosion rate at the watershed scale in southern Taiwan estimated from magnitude and frequency of rainfall

This study calculated the long-term average landslide erosion rate in the Kaoping River watershed in southern Taiwan and investigated the relative importance of extreme rainfall events on landslide erosion. The method followed three steps: first, calculating landslide volumes for 10 rainfall events from a multi-temporal, event-based landslide inventory; second, estimating the frequency of landslide-generating rainfall by using hydrologic frequency analyses; and third, combining the two sets of data to estimate the average landslide erosion rate. Results of the study showed that the average landslide erosion rate is 2.65–5.17mmyr−1, corresponding well to rates reported in other studies using other methods. The study also found that extreme-intensive rainfall events play a more important role on landslide erosion than frequent-moderate rainfall events. Extreme rainfall (maximum 24-h rainfall >600mm) contributes 64–79% of the average landslide erosion rate. Moreover, the natural variation of landslide erosion magnitudes is extremely large and can cause significant uncertainty in estimating the landslide erosion rate from total landslide volume. This study found ±1.2mmyr−1 of uncertainty based on simulation results involving a hypothetical 100-year landslide inventory. In summary, this study demonstrates the importance of extreme rainfall events on landslide erosion, and the method proposed in this study is capable of calculating a reliable estimate of average landslide erosion rate in areas with insufficient landslide records.

Landslide volumes and landslide mobilization rates in Umbria, central Italy

A catalogue of 677 landslides of the slide type was selected from a global database of geometrical measurements of individual landslides, including landslide area ( A L) and volume ( V L). The measurements were used to establish an empirical relationship to link A L (in m 2) to V L (in m 3). The relationship takes the form of a power law with a scaling exponent α = 1.450, covers eight orders of magnitude of A L and twelve orders of magnitude of V L, and is in general agreement with existing relationships published in the literature. The reduced scatter of the experiential data around the dependency line, and the fact that the considered landslides occurred in multiple physiographic and climatic environments and were caused by different triggers, indicate that the relationship between V L and A L is largely independent of the physiographical setting. The new relationship was used to determine the volume of individual landslides of the slide type in the Collazzone area, central Italy, a 78.9 km 2 area for which a multi-temporal landslide inventory covering the 69-year period from 1937 to 2005 is available. In the observation period, the total volume of landslide material was V LT = 4.78 × 10 7 m 3, corresponding to an average rate of landslide mobilization φ L = 8.8 mm yr − 1 . Exploiting the temporal information in the landslide inventory, the volume of material produced during different periods by new and reactivated landslides was singled out. The wet period from 1937 to 1941 was recognized as an episode of accelerated landslide production. During this 5-year period, approximately 45% of the total landslide material inventoried in the Collazzone area was produced, corresponding to an average rate of landslide mobilization φ L = 54 mm yr − 1 , six times higher than the long term rate. The volume of landslide material in an event or period was used as a proxy for the magnitude of the event or period, defined as the logarithm (base 10) of the total landslide volume produced during the event, or period. With this respect, the new relationship to link A L and V L is a starting point for the adoption of a quantitative, process based landslide magnitude scale for landslide events.

Effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central Japan

AbstractLandslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention. We examined the effects of forest harvesting on the frequency of landslides and debris flows in the Sanko catchment (central Japan) using nine aerial photo periods covering 1964 to 2003. These photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912. Geology and slope gradient are rather uniformly distributed in the Sanko catchment, facilitating assessment of forest harvesting effects on mass wasting without complication of other factors. Trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery; the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting. Sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10‐fold higher than in control sites. Total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5·8 × 103 m3 km−2 compared with 1·3 × 103 m3 km−2 in clearcuts >25 yr, indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability. Because landslide scars continue to produce sediment after initial failure, sediment supply from landslides continues for 45 yr in the Sanko catchment. To estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions, changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions. Copyright © 2007 John Wiley & Sons, Ltd.

Slope stabilization and landslide size on Mt. 99 Peaks after Chichi Earthquake in Taiwan

The study focuses on the landslide characteristics of Mt. 99 Peaks in Nantou County, the most serious landslide prone area caused by Chichi Earthquake in Taiwan. Several investigations and field surveys were made on Mt. 99 Peaks for 5 years to research the landslide area and depth, rainfall trend, and slope stabilization. The total landslide volume caused by the earthquake on Mt. 99 Peaks was about 1.47×106 m3 and the mean landslide thickness was about 0.22 m. Gravel layers with a volume of more than 80% of total soil profile dominated Mt. 99 Peaks. The landslide on Mt. 99 Peaks was induced by heavy rainfall from July to September because the rainfall on Mt. 99 Peaks had a nonuniform distribution in time. Although the vegetation recovery on Mt. 99 Peaks was in progress, the soil slope had remained unstable. As a result, Typhoon Mindulle occurred in July 2004 collapsed the hillslope again after 5 years of Chichi Earthquake. This study suggests that vegetation recovery on Mt. 99 Peaks for 5 years was insufficient to stabilize the landslide affected area.

Contribution of deep‐seated bedrock landslides to erosion of a glaciated basin in southern Alaska

AbstractLandslides represent a key component of catchment‐scale denudation, though their relative contribution to the erosion of glaciated basins is not well known. Bedrock landslide contribution was investigated on the surface of one of eleven glaciers on a glaciated ridge in the Chugach‐St Elias Range of southern Alaska, where the debris from four major landslides is easily distinguished from moraines and other supraglacial material. A series of aerial and satellite photos from 1972 to 2000 and field observations in 2001 and 2002 indicate that three of four landslides have fallen onto the surface of the glacier since about 1978. The landslides, which originated from the steeply dipping (60–70°) bedrock walls, were deposited onto the glacier in the ablation zone and are currently being transported downstream supraglacially. Individual glacial valleys with topographic relief of ∼400 m are cut into high‐grade metamorphic rock characterized by a steep north‐dipping foliation and fractured by numerous large joints. Measurements of landslide area and average thickness obtained from high‐resolution survey data indicate a total landslide volume of ∼2·3 × 105 m3. This volume suggests a basin‐averaged erosion rate from landslides of 0·48 mm a−1. An overall basin‐scale erosion rate of 0·7 to 1·7 mm a−1 can be inferred, but depends on the percentage of the total‐basin sediment yield contributed by supraglacial sources. A mean rockwall retreat rate of 6·7 mm a−1 is calculated and is considerably higher than published rates, which range from 0·04 to 4·0 mm a−1. Controls on landslide generation include seismicity, freeze–thaw processes, topography, rock strength, and debuttressing. It is likely all of these factors contribute to failure, although the primary controls for the landslides in this study are thought to be rock strength and topography. The absence of landslides on ten of the eleven glaciers on this ridge is attributed to landslide magnitude–frequency relationships and short temporal scale of this study. Large‐volume bedrock landslides (>100 000 m3) may have low frequency, occurring less than once in a 55‐year time frame. Copyright © 2005 John Wiley & Sons, Ltd.

Long‐term modelling of landslides for different forest management practices

AbstractLong‐term effects of different forest management practices on landslide initiation and volume were analysed using a physically based slope stability model. The watershed‐based model calculates the effects of multiple harvesting entries on slope stability by accounting for the cumulative impacts of a prior vegetation removal on a more recent removal related to vegetation root strength and tree surcharge. Four sequential clearcuts and partial cuts with variable rotation lengths were simulated with or without leave areas and with or without understorey vegetation in a subwatershed of Carnation Creek, Vancouver Island, British Columbia. The combined infinite slope and distributed hydrologic models used to calculate safety factor revealed that most of the simulated landslides were clustered within a 5 to 17 year period after initial harvesting in cases where sufficient time (c. 50 years) lapsed prior to the next harvesting cycle. Partial cutting produced fewer landslides and reduced landslide volume by 1·4‐ to 1·6‐fold compared to clearcutting. Approximately the same total landslide volume was produced when 100 per cent of the site was initially clearcut compared to harvesting 20 per cent of the area in successive 10 year intervals; a similar finding was obtained for partial cutting. Vegetation leave areas were effective in reducing landsliding by 2‐ to 3‐fold. Retaining vigorous understorey vegetation also reduced landslide volume by 3·8‐ to 4·8‐fold. The combined management strategies of partial cutting, increasing rotation length, provision of leave areas, and retention of viable understorey vegetation offer the best alternative for minimizing landslide occurrence in managed forests. Copyright © 2003 John Wiley & Sons, Ltd.