Landslide-dammed Lake Research Articles

Age constraints and paleoseismic implication of rock avalanches in the northern Patagonian Andes, Argentina

Landslides and rock avalanches are far more common features than once believed in the glacial valleys of the northern Patagonian Andes of Argentina. We describe three rock avalanches located in northwestern Neuquén province that generated landslide-dammed lakes. Cosmogenic radionuclide 36Cl dating constrains their average ages as Late Pleistocene for the Lagunas de Varvarco rock avalanches (79.0 ± 3.0–63.0 ± 3.0 ka and 37.0 ± 1.8–29.0 ± 1.5 ka) and Holocene (2.2 ± 0.6 ka) for the Barrancas avalanche. The landslide dam originated by the Barrancas rock avalanche became unstable on December 29, 1914, causing a devastating outburst flood. These phenomena indicate rock volumes greater than 5 × 10 5 m 3 each, and the Varvarco Campos rock avalanche (3.51 × 10 9 m 3) is the largest rock avalanche recognized in Argentina. The rock avalanches described here occurred after the glacial retreat. The volume of the landslides and the matching of these gravitational phenomena with current seismicity data, as well as other morphometric, lithologic, and structural characteristics, suggest that these rock avalanches likely were triggered by earthquakes. On the basis of empirical relations, we postulate that the Varvarco Campos rock avalanche testifies to a paleoearthquake of magnitude ( M > 8), much larger than the events recorded by instrumental seismicity ( M ⩽ 5.8).

Pleistocene lake outburst floods and fan formation along the eastern Sierra Nevada, California: implications for the interpretation of intermontane lacustrine records

Variations in the rock flour fraction in intermontane lacustrine sediments have the potential to provide more complete records of glacier fluctuations than moraine sequences, which are subject to erosional censoring. Construction of glacial chronologies from such records relies on the assumption that rock flour concentration is a simple function of glacier extent. However, other factors may influence the delivery of glacigenic sediments to intermontane lakes, including paraglacial adjustment of slope and fluvial systems to deglaciation, variations in precipitation and snowmelt, and lake outburst floods. We have investigated the processes and chronology of sediment transport on the Tuttle and Lone Pine alluvial fans in the eastern Sierra Nevada, California, USA, to elucidate the links between former glacier systems located upstream and the long sedimentary record from Owens Lake located downstream. Aggradation of both fans reflects sedimentation by three contrasting process regimes: (1) high magnitude, catastrophic floods, (2) fluvial or glacifluvial river systems, and (3) debris flows and other slope processes. Flood deposits are represented by multiple boulder beds exposed in section, and extensive networks of large palaeochannels and boulder deposits on both fan surfaces. Palaeohydrological analysis implies peak discharges in the order of 10 3–10 4 m 3 s −1, most probably as the result of catastrophic drainage of ice-, moraine-, and landslide-dammed lakes. Cosmogenic radionuclide surface exposure dating shows that at least three flood events are represented on each fan, at 9–13, 16–18 and 32–44 ka (Tuttle Fan); and at ∼23–32, ∼80–86 ka, and a poorly constrained older event (Lone Pine Fan). Gravels and sands exposed in both fans represent fluvial and/or glacifluvial sediment transport from the Sierra Nevada into Owens Valley, and show that river systems incised and reworked older sediment stored in the fans. We argue that millennial-scale peaks in rock flour abundance in the Owens Lake core reflect (1) fluctuations in primary subglacial erosion in the catchments in response to glacier advance–retreat cycles; (2) short-lived pulses of sediment delivered directly by catastrophic flood events; and (3) sediment released from storage in alluvial fans by fluvial and glacifluvial incision and reworking. As a result of this complexity the coarse sediment peaks in lake deposits may not simply reflect periods of increased glaciation, but likely also reflect changes in sediment storage and flux controlled by paraglacial processes. Current dating evidence is inadequate to allow precise correlation of individual flood or incision events with the Owens Lake rock flour record, although given the widespread occurrence of flood deposits in fans along the eastern margins of the Sierra Nevada, it is clear that fan deposition and incision played a very important role in modulating the delivery of glacigenic sediment to Owens Lake.

Late Quaternary intensified monsoon phases control landscape evolution in the northwest Himalaya

The intensity of the Asian summer-monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes, terrestrial environments, and marine sedi- ment records. However, the mechanisms of long-lived (2-5 k.y.) intensified monsoon phases, the related changes in precipitation distribution, and their effect on landscape evolution and sedimen- tation rates are not yet well understood. The arid high-elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal (i.e., strength- ened) monsoon seasons. Analogous to present-day rainfall anom- alies, enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure. We as- sociate landslide triggering during intensified monsoon phases with enhanced precipitation, discharge, and sediment flux leading to an increase in pore-water pressure, lateral scouring of rivers, and ov- ersteepening of hillslopes, eventually resulting in failure of slopes and exceptionally large mass movements. Here we use lacustrine deposits related to spatially and temporally clustered large land- slides (.0.5 km 3 ) in the Sutlej Valley region of the northwest Him- alaya to calculate sedimentation rates and to infer rainfall patterns during late Pleistocene (29-24 ka) and Holocene (10-4 ka) inten- sified monsoon phases. Compared to present-day sediment-flux measurements, a fivefold increase in sediment-transport rates re- corded by sediments in landslide-dammed lakes characterized these episodes of high climatic variability. These changes thus em- phasize the pronounced imprint of millennial-scale climate change on surface processes and landscape evolution.

Signature of Rhine Valley sturzstrom dam failures in Holocene sediments of Lake Constance, Germany

Landslide-dammed lakes that form upstream of large-scale rockslide-avalanches (=sturzstroms) present an enormous potential hazard to downstream areas. Such failures are recorded in the Early Holocene sediments of Upper Lake Constance (Germany) by the presence of two clastic layers that were emplaced around 9400 cal. YBP. The sedimentology of these layers contrasts sharply with the typical Late Glacial and Holocene lacustrine sediments present beneath the floor of the lake. Sedimentary structures and the magnetic fabric of these clastic deposits strongly suggest that they were emplaced by hyperpycnal underflows related to catastrophic floods that entered the lake from the Rhine River. From stratigraphic and geologic data, it is inferred that the hyperpycnite deposits are directly related to the failure of two sturzstrom dams and the draining of the dammed lakes that developed upstream from them. These lakes were dammed by the Flims and the Tamins sturzstrom deposits, respectively. Sedimentologic data from Lake Constance indicate that the two successive events occurred within a very short time interval, probably not exceeding several years. Consequently, these lacustrine deposits provide essential information about the morphogenic evolution of the Rhine River valley during the Early Holocene and about the sturzstrom events that occurred during the same time interval.

Rock avalanching into a landslide-dammed lake causing multiple dam failure in Las Conchas valley (NW Argentina) ? evidence from surface exposure dating and stratigraphic analyses

Generally landslide dams which exist for several hundreds to thousands of years are considered as stable. We show with an example from the Argentine Andes that such dams can exist for several thousands of years but still may fail catastrophically. Multiple rock avalanches impounded two lakes with surface areas of ~8 km2 and ~600 km2, respectively, in Las Conchas valley, NW Argentina. Surface exposure dating (SED) by 10Be of the rock-avalanche deposits or landslide scars indicates that these landslides occurred at 15,300±2,000 yr and 13,550±900 yr. The dams were stable during a strong earthquake, as suggested by seismites within related lake sediments and by multiple coeval landslides in this region, which occurred at ~7.5 kyr. However, when a further rock-avalanche fell into the lower, smaller lake at 4,800±500 yr the dam downriver was destroyed, presumably by the resulting tsunami wave. The resulting flood also destroyed an additional rock-fall dam which had formed at ~5,630 yr 14C cal BP 30 km downriver. The new dam formed by the second rock avalanche was eroded prior to 3,630 yr 14C cal BP. This dam erosion coincides with an important climatic shift towards more humid conditions in the Central Andes. Our results show that instead of direct effects of strong seismicity on landslide dams, (1) landsliding into a landslide-dammed lake, (2) abrupt hydrological changes, and (3) climate change towards conditions related to enhanced run-off are processes which can produce failures of “quasi-stable” natural dams.

Geomorphometric characteristics of New Zealand landslide dams

This study presents results from a quantitative analysis of a new inventory of n=232 landslide dam occurrences in New Zealand. Previously published data were expanded by documentation of recent events and evidence from a regional air-photo reconnaissance focused on the upland regions of southwestern South Island. Additional geomorphometric data on landslide dams, associated lakes, and contributing catchment characteristics, were extracted from a 25-m Digital Elevation Model (DEM), augmented by limited ground truthing, and compiled in a GIS-based inventory. The New Zealand case examples fall into the global trend, although they contain both two extremely large features in terms of landslide dam volume V D and lake volume V L. Analysis suggests that landslide dam height H D, landslide dam volume V D, lake volume V L, contributing catchment area A C, and local relief H R, are key variables for assessing landslide dam stability independently from other catchment parameters such as lithology, climate, or dam sedimentology. They may be provisionally used as representative characteristics of landslide dams, irrespective of environmental boundary conditions, such as climate, geology, or site-specific valley geomorphometry. Three newly proposed dimensionless indices, i.e., the Backstow Index I s, Basin Index I a, and Relief Index I r, based on landslide dam height H D allow limited, yet promising, preliminary assessments of landslide dam stability. Compared with worldwide examples, they also demonstrate a much narrower conditional range for the formation of stable landslide dams in New Zealand. Catchment parameters such as maximum elevation E max, upstream relief H R, contributing catchment area A C, and relief ratio R R are significantly different at sites of former and existing landslide-dammed lakes, and may be used as independent variables in future terrain-based classification schemes. Generally, data are incomplete with underreporting of small and ephemeral landslide dams, and over-representation of earthquake case studies. Nonparametric correlation highlights the statistical interdependence between geomorphometric variables as an artefact of initial data calculation, while varying accuracy poses a significant drawback for complex multivariate statistical techniques such as principal component, cluster, or discriminant analyses.

Multiple landslide clusters record Quaternary climate changes in the northwestern Argentine Andes

The chronology of multiple landslide deposits and related lake sediments in the semi-arid eastern Argentine Cordillera suggests that major mass movements cluster in two time periods during the Quaternary, i.e. between 40 and 25 and after 5 14C kyr BP. These clusters may correspond to the Minchin (maximum at around 28–27 14C kyr BP) and Titicaca wet periods (after 3.9 14C kyr BP). The more humid conditions apparently caused enhanced landsliding in this environment. In contrast, no landslide-related damming and associated lake sediments occurred during the Coipasa (11.5–10 14C yr BP) and Tauca wet periods (14.5–11 14C yr BP). The two clusters at 40–25 and after 5 14C kyr BP may correspond to periods where the El Niño–Southern Oscillation (ENSO) and Tropical Atlantic Sea Surface Temperature Variability (TAV) were active. This, however, was not the case during the Coipasa and Tauca wet periods. Lake-balance modelling of a landslide-dammed lake suggests a 10–15% increase in precipitation and a 3–4°C decrease in temperature at ∼30 14C kyr BP as compared to the present. In addition, time-series analysis reveals a strong ENSO and TAV during that time. The landslide clusters in northwestern Argentina are therefore best explained by periods of more humid and more variable climates.

The July 29, 1998, debris flow and landslide dam at Capricorn Creek, Mount Meager Volcanic Complex, southern Coast Mountains, British Columbia

A very large debris flow was triggered during a period of record-breaking high temperatures in upper Capricorn Creek, within the Mount Meager Volcanic Complex, a part of the Garibaldi Volcanic Belt of the southern Coast Mountains. The debris flow deposit impounded Meager Creek, creating an 800 m long landslide-dammed lake. The total event volume was 1.2 × 106 m3. The debris flow was followed by three days of almost continuous hyperconcentrated flow surges, which caused significant fluvial aggradation in the Meager Creek flood plain below the Capricorn Creek confluence. Within a few days of the formation of the landslide dam, a spillway notch had been cut through the deposit, thereby preventing the occurrence of a catastrophic dam break. The landslide, which triggered the debris flow, originated in deep volcanic colluvium having a previous history of progressive slope deformation, a consequence of glacial downwasting since the Neoglacial maximum. This paper highlights an important landslide response to recent glacial retreat and suggests that similar events could reoccur within Capricorn Creek, as well as at other sites where steep colluvial and weak bedrock slopes have been glacially debuttressed.

Formation of landslide-dammed lakes during a wet period between 40,000 and 25,000 yr B.P. in northwestern Argentina

New AMS radiocarbon data from the deposits of landslide-dammed lakes in the Santa Maria Basin (26°S, 66°W) and the Quebrada del Toro (25°S, 66°W) in the eastern Argentine Cordillera show that important mass movements occurred during a wet period between 40,000 and 25,000 yr B.P. In addition to increased humidity during this time, detailed analysis of annual-layered lacustrine strata suggests enhanced inter- and intra-annual fluctuations in precipitation as compared to the present. Variations in sediment characteristics and diatom assemblages with mean periodicities of 2 to 5 and 10 to 14 years, respectively, suggest an influence of the El Niño/Southern Oscillation (ENSO) and the Atlantic sea-surface temperature dipole. The Atlantic dipole slightly increased rainfall every 10–14 years as at present. In contrast, the weak modern ENSO influence in this area differs from the past situation where rainfall increased significantly with ENSO-type periodicities. Both increased humidity and seasonality are believed to have reduced thresholds for the generation of catastrophic mass movements in northwestern Argentina.

Landslide-dammed lakes: a case study of the Lamabagar and Chaunrikharka landslide deposits, Dolakha and Solukhumbu districts, eastern Nepal

The Lamabagar and Chaunrikharka landslides occurred within the gneisses of the Higher Himalayan lithotectonic unit both about 10 km north of the Main Central Thrust (MCT). Both landslide deposits are in the range of 10 to 100 million m3 and show an abnormal long stability, which confirms that the big size, the cohesiveness of the material and quick siltation of the impoundment are the most important factors for the longevity of natural dams. The Lamabagar landslide dam (Fig. 1) with a height of about 300 m is standing since more than three generations and the impoundment is completely silted up. The relics of the early postglacial Cbaunrikharka landslide dam (Fig. 2) with a former height of about 100 m and the eroded lake sediments of the Gath-Phakting area exposes excellently its inventory. The most probably annually layered bottom-set sediments south of Gath indicate a lifetime of the dam of about 120 years. Terraces within the canyon of Chaunrikharka document a periodical downcutting of the dam. The stable landslide dam of Lamabagar represents a prospective site for a hydroelectric plant of about 30MW.

Ancient landslide-dammed lakes in southeastern Sicily and their presumable contribution to malaria development: a poorly known effect of local seismicity

Ancient landslide-dammed lakes in southeastern Sicily and their presumable contribution to malaria development: a poorly known effect of local seismicity

Late Pleistocene landslide-dammed lakes along the Rio Grande, White Rock Canyon, New Mexico

Massive slump complexes composed of Pliocene basaltic rocks and underlying Miocene and Pliocene sediments flank the Rio Grande along 16 km of northern White Rock Canyon, New Mexico. The toe area of at least one slump complex was active in the late Pleistocene, damming the Rio Grande at least four times during the period from 18 to 12 {sup 14}C ka and impounding lakes that extended 10-20 km upriver. Stratigraphic relationships and radiocarbon age constraints indicate that three separate lakes formed between 13.7 and 12.4 {sup 14}C ka. The age and dimensions of the ca. 12.4 ka lake are best constrained; it had an estimated maximum depth of {approx}30 m, a length of {approx}13 km, a surface area of {approx}2.7 km{sup 2}, and an initial volume of {approx}2.5 x 10{sup 7} m{sup 3}. The youngest landslide-dammed lakes formed during a period of significantly wetter regional climate, strongly suggesting that climate changes were responsible for reactivation of the slump complexes. We are not certain about the exact triggering mechanisms for these landslides, but they probably involved removal of lateral support due to erosion of the slope base by the Rio Grande during periods of exceptionally high flood discharge or rapid incision;more » increased pore pressures associated with higher water tables; higher seepage forces at sites of ground-water discharge; or some combination of these processes. Seismic shaking could also have contributed to triggering of some of the landslides, particularly if aided by wet antecedent conditions. 54 refs., 19 figs., 3 tabs.« less

Recent Holocene changes in sedimentation in a landslide-dammed lake in the Cascade Mountains, southwestern British Columbia, Canada

Landslide-damming of Silver Lake in the Cascade Mountains took place about 1000BP. Delta growth favoured the faulted west valley side. At the commencement of logging activity in AD 1946 the course of Silverhope Creek was diverted away from access roads. As a consequence, the channel shifted from the west to the east side of the valley, forming a new delta. Six gravity lake cores and SCUBA surveys of lake sediments reveal changes in the depositional regime. In two cores, late Pleistocene-early Holocene sediments are pre served. Old delta abandonment, new delta growth, reorientation of turbidity channels and confluence zones are discussed. 137Cs data show that, following channel diversion, little or no further deposition occurred on the old delta. Assuming that the 1964 137Cs maximum has been recorded in each core, sedimentation rates appar ently decrease to the NNW, away from the new delta, and 137Cs values increase northwards. Stratigraphy, 14C and 137Cs dates indicate that there has been a recent increase in sedimentation rate of about 20 times near the deltas, to about 10 times in a mid-lake location. Erosion and the release of destabilized glaciolacustrine valley- side sediments into the creek enhances sedimentation in Silver Lake. Unstable sediments on steep valley sides prohibit forest regrowth.

Valtellina Landslide and Flood Emergency, Northern Italy, 1987

This report describes the progress of the landslide and flood emergency that occurred in Valtellina, in the northern Italian Alps, during July and August 1987. For the authorities, the critical problem was one of controlling the rise of a large lake impounded on the River Adda by landslide debris that threatened to breach catastrophically, releasing a major floodwave. Several lessons can be learned from the way in which the emergency was managed. First, helicopters played a critical role in evacuating survivors and moving supplies around the disaster area, but there was scope for better co-ordination of operations. Secondly, high levels of private car ownership allowed greater flexibility in designing mass evacutation plans for threatened communites, but such high personal mobility proved difficult to control in order to ensure public safety. In future, education programmes could be used to help people appreciate the dangers of driving during periods of great natural hazard risk. Thirdly, the Valtellina disaster coincided with a change of national government, including substitution of the Minister of Civil Protection. This led to a policy vacuum, sub-optimal decision making and erosion of public confidence in political leaders. Landslide-dammed lakes represent a widespread but rather unpredictable hazard: they therefore require flexible emergency repsonse, but not without decisive leadership.

Effects of earthquake-induced landslides on sediment budget and transport over a 50-yr period

Landsliding during a magnitude 7.7 earthquake in 1929 in northwestern South Island, New Zealand, delivered up to ∼400 000 m 3 /km 2 of sediment to stream channels. First- to third-order channels were buried to depths of as much as 10 m with sedimentary rock debris for distances ranging from 2 of the 92-km 2 study area because of the coarse grain size of the sedimentary rock debris and trapping of sediment in numerous landslide-dammed lakes. Sand- and pebble-sized debris originating from landslides on a 6.6-km 2 area of granite has been transported downstream no more than ∼10 km. At least 50% to 75% of this granitic debris is retained in the fourth-order 92-km 2 catchment 50 yr after the earthquake. The long retention times of sediment and the volume of debris supplied by landslides during a large earthquake suggest that earthquake-induced landsliding is the principal sediment-supply mechanism in the region.

Field reconnaissance of the effects of the earthquake of April 13, 1973, near Laguna de Arenal, Costa Rica

abstract The April 13, 1973, earthquake (MS = 6.5) in northwestern Costa Rica caused significant damage and the loss of 23 lives in a rural area of about 150 km2 centered south of Laguna de Arenal. Earthquake-triggered failures of mountain slopes were the cause of all deaths and injuries attributable to the earthquake. Incipient landslides and landslide-dammed lakes pose a continuing hazard to populated areas at Tronadora and Rio Chiquito during the 1973 rainy season. The modest amount of shaking damage to structures is attributable to the moderate size of the earthquake and to the predominance of small wood-frame buildings with lightweight corrugated roofs that have good shear resistance to lateral forces. Most of the structural damage that did occur was to buildings made of concrete block with little or no reinforcing steel; none of these, however, involved total collapse. In some areas, damage to buildings and roads was also caused by foundation failures involving downslope slumping or sliding, lateral spreading, and differential compaction of unconsolidated or poorly consolidated surficial deposits including thick lateritic soil. The location of the epicentral region and the nature of the earthquake and aftershock sequence suggest that the earthquake was of tectonic, rather than volcanic, origin. The shape and size of the damage area and the apparent absence of surface faulting are compatible with a moderately shallow source, possibly several kilometers in depth.