Robert L. Schuster

Usoi Landslide Dam and Lake Sarez, Pamir Mountains, Tajikistan

In 1911, a 2-km 3 (0.5-mi 3 ) earthquake-triggered rock slide blocked the Murgab River, southeastern Tajikistan, forming a still-existing, 600-m-high (1,970-ft-high) natural dam—the highest dam, natural or man-made, in the world. Lake Sarez, impounded by this blockage, is 60 km (37 mi) long, with a maximum depth of 550 m (1,800 ft) and a volume of approximately 17 km 3 (∼4 mi 3 ). This lake, which has never overtopped the dam, exits the downstream face as a series of large springs that regroup as the Murgab River. Freeboard between lake surface and the lowest point on the dam crest currently is approximately 50 m (∼165 ft), and the lake is rising at an average rate of 18.5 cm/yr (7.3 in./yr). If the blockage were to fail, a worst-case scenario could endanger tens or possibly hundreds of thousands of people in the Murgab, Bartang, Panj, and Amu Darya valleys downstream. Dam failure potentially could result from: 1) seismic shaking, 2) catastrophic overtopping caused by a landslide entering the lake from the valley wall at high velocity, 3) surface erosion caused by natural overtopping by the rising lake, 4) internal erosion (piping), 5) instability caused by lake pressure against the dam, or 6) slope instability of the dam faces. Occurrence of an overtopping wave resulting from a potential landslide high on the right bank of Lake Sarez seems to be the most realistic of these slight possibilities for failure. Because of the high cost of installing physical remediation to the dam in this rugged mountain area (no roads lead to the site), the main protective measures now being undertaken are hydrological monitoring at the dam and installation of a flood early warning system downstream.

The 1985 Bairaman landslide dam and resulting debris flow, Papua New Guinea

Abstract On 11 May 1985 a magnitude 7.1 (Richter scale) earthquake occurred on the island of New Britain, Papua New Guinea. The earthquake caused localized property damage and initiated widespread landsliding up to 30 km from the epicentre. One of the largest landslides, with an estimated volume of 180 x 106m3, occurred in the narrow, steep-sided Bairaman River valley. This landslide started as a rockslide in weathered limestone and rapidly transformed into a debris avalanche, filling over 3 km of the Bairaman River valley to a maximum depth of 200 m and creating a landslide dam which impounded the Bairaman River. By August 1986 the resultant lake had attained a volume of about 50 x 106 m3 and posed a grave threat to downstream inhabitants of the Bairaman valley. By September 1986 the lake was close to overtopping, the people were evacuated and the dam was breached. The failure of the dam took about 3 hours and generated a debris flow with an estimated volume of 120 x 106 m3 and average velocity of 20 km h-1 that travelled 39 km down the Bairaman valley to the Solomon Sea. At the river mouth the flood was 8 m above normal river level and swept away Bairaman village. Due to the evacuation no lives were lost.

Mass wasting triggered by the 5 March 1987 ecuador earthquakes

On 5 March 1987, two earthquakes (Ms = 6.1 and Ms = 6.9) occurred about 25 km north of Reventador Volcano, along the eastern slopes of the Andes Mountains in northeastern Ecuador. Although the shaking damaged structures in towns and villages near the epicentral area, the economic and social losses directly due to earthquake shaking were small compared to the effects of catastrophic earthquake-triggered mass wasting and flooding. About 600 mm of rain fell in the region in the month preceding the earthquakes; thus, the surficial soils had high moisture contents. Slope failures commonly started as thin slides, which rapidly turned into fluid debris avalanches and debris flows. The surficial soils and thick vegetation covering them flowed down the slopes into minor tributaries and then were carried into major rivers. Rock and earth slides, debris avalanches, debris and mud flows, and resulting floods destroyed about 40 km of the Trans-Ecuadorian oil pipeline and the only highway from Quito to Ecuadors northeastern rain forests and oil fields. Estimates of total volume of earthquake-induced mass wastage ranged from 75–110 million m3. Economic losses were about US

Engineering Measures for the Hazard Reduction of Landslide Dams

1 billion. Nearly all of the approximately 1000 deaths from the earthquakes were a consequence of mass wasting and/or flooding.

Landslide Hazards and Their Reduction

Landslide dams cause two types of floods: (1) upstream flooding as the impoundment fills, and (2) downstream flooding resulting from catastrophic failure of the dam. A landslide dam may last for a few hours or for thousands of years, depending on: (1) rate of inflow to the lake (2) size and shape of the dam (3) physical character of the materials that comprise the dam, and (4) rate of seepage through the dam. This paper discusses (1) modes of flooding resulting from landslide dams (2) characteristics of failure of landslide dams (3) mitigative (i.e., remedial) measures used to reduce flood hazards from landslide dams, and (4) case histories in which mitigative measures have been used, both successfully and unsuccessfully. Mitigative engineering measures can reduce the hazard associated with landslide dams by preventing the failure of most landslide dams, or at least by reducing the severity of possible flooding.

Economic Losses and Fatalities Due to Landslides

Abstract Landslides are a widespread and costly problem in many parts of the United States. Although reliable estimates of the costs of landslide damage are difficult to obtain, a conservative estimate of the present-day direct and indirect costs of slope failures in the United States exceeds

Documented historical landslide dams from around the world

1 billion annually. Losses from landslides can be significantly reduced by the cooperative effort of geologists, engineers, and planners, clearly demonstrating the value of loss mitigation measures. A program to reduce the losses from landslides in the hillside areas of Los Angeles has been in effect since 1952 and, by one method of evaluation, has reduced losses by nearly a factor of 50.