USGS scientists with Venezuelan military liaisons.

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Stuart Oliver
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2 USGS scientists with Venezuelan military liaisons.

3 In December, 1999, heavy rainfall triggered thousands of debris flows and caused numerous flash floods in a 300- kilometer long area of the north coast of Venezuela. The death toll is estimated at 30,000 people.

4 Principal regional controls on weather in Venezuela between December 1 and 19, 1999.

5 Precipitation was 40 to 50 percent above normal in most of the eastern Caribbean during 1999.

6 Rainfall amounts of 300 to 480 mm over the towns of Maiquetía and La Guaira on the coast north of Caracas, Venezuela, between Dec. 15, 1800 UTC and Dec. 17, 1200 UTC, were estimated from NOAA-NESDIS Autoestimator, using GOES 8 satellite data.

7 Venezuelan government damage estimates by drainage basin: red = very severe; yellow = severe; tan = moderate; white = low

8 Satetellite image and topographic map of coast between airport and Caraballeda. Gray areas are mainly freshly exposed bedrock and sediment but also include concrete structures. Note pronounced scour of river channel south of Caraballeda (Quebrada San Julián), eroded hillslopes and alluvial fan deposition.

9 Vargas state showing abundant debris-flow scars, fresh sediments in river canyons and on alluvial fans, areas of recent seaward progradation of fans, and sediment plumes.

10 Oblique view to south before the December 1999 disaster, showing El Avila mountains, Quebrada San Julián drainage basin, and coastal urbanization near Caraballeda, Vargas state, Venezuela.

11 Caraballeda alluvial fan. Upstream drainage area is about 28 square kms, relief about 2 kilometers, with fluvial system average slope as high as 50 percent. Flow energy is enhanced by acceleration through the narrow canyon.

12 Quebrada San Julián showing the high slope angles, large numbers of debris flow scars and abundance of new alluvium and colluvium in the channel bed and fan surface.

13 Debris flow scars along Quebrada San Julián; Río Naiguatá across alluvial fan in newly widened channel at Naiguatá.

14 Caraballeda looking southwest showing newly opened channels in foreground and center right of photograph.

15 Los Corales sector of Caraballeda. Debris flows and sediment-laden flash floods destroyed or damaged most structures on this alluvial fan.

16 Los Corales sector of Caraballeda showing damage to apartment building.

17 Debris flows passed through the 3rd story of this apartment building in Los Corales sector of Caraballeda.

18 Boulder transported by debris flow of Dec.1999, Caraballeda.

19 Tanaguarena. This community is located at confluence of multiple natural hazards.

20 Carmen de Uria: this narrow canyon and alluvial fan has no areas that are not either susceptible to flooding or to landslides. The loss of life in this community was great.

21 Carmen de Uria: Before the December storm, the housing density in center equaled that on the left side.

22 Remains of houses damaged by flash floods and landslides of December,1999: Carmen de Uria.

23 Lens-shaped exposure of a debris-flow deposit beneath 5 m of more recent alluvial sediment, Carmen de Uria.

24 Mudlines on buildings indicate maximum water level during flash flood. Degree of turbulence is apparent in the uneven elevation of the lines.

25 Because of the great susceptibility to flash flooding and Landslides in Carmen de Uria, the town remains will likely be demolished and no re-occupation will be permitted.

26 Debris flow and flash flood damage to Universidad Simón Bolívar campus, located on alluvial fan at canyon mouth.

27 Debris flow and flash flood damage to Universidad Simón Bolívar campus. One-story buildings in foreground are buried to rooftops with sediment.

28 Debris flow scars upstream of Caraballeda. Most sand, silt, clay derived from the debris flows was transported offshore. The coarse-sized gray and white sediment that now covers the canyon floor is derived from bedrock exposed on hillslopes and channels upstream.

29 Debris-flow scars, remains of houses and two-lane highway on Caribbean coast.

30 Hundreds of landslides destroyed or damaged sections of the coast road near Los Camuri.

31 Naiguata: Hillslope denudation by debris flows was extensive in some coastal regions. 30 m tall pylon for scale.

32 San Francisco de Galipán in El Avila National Park. These 38 debris flow scars in otherwise undisturbed forest show the storm of December 1999 was of unusually high magnitude.

33 Debris flow scars in San Francisco de Galipán in the El Avila National Park.

34 Effects of debris-flow in San Francisco de Galipán in the El Avila National Park. This debris flow killed several people in the house on the left.

35 Debris-flow deposits in channel at San José de Galipán in the El Avila National Park. Massive amounts of sediment that will be mobilized during future storms remains in channels and on landslide scars.

36 Local residents cutting drainage ditches in road surface to divert runoff in area where damage by landslides was extensive. (San José de Galipán in the El Avila National Park)

37 Naiguata: This pleasure-boat marina was filled with sediment by debris flows and flash floods.

38 Flash floods damaged hundreds of containers at the seaport in Maiquetía

39 Flash flood damage halted operations at the Maiquetía seaport and hampered efforts to bring in emergency supplies immediately after the disaster of December, 1999.

40 Flash flood damage to seaport at Maiquetía. Hazardous materials in some containers were leaked into the ground and into the sea.

Debris flow: categories, characteristics, hazard assessment, mitigation measures. Hariklia D. SKILODIMOU, George D. BATHRELLOS

Debris flow: categories, characteristics, hazard assessment, mitigation measures Hariklia D. SKILODIMOU, George D. BATHRELLOS Natural hazards: physical phenomena, active in geological time capable of producing