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Matthew C. Larsen

Publications and source records attributed to Matthew C. Larsen.

At least 37 records · Page 2Linked to original sources
USGS2002

Debris-flow and flooding deposits in coastal Venezuela associated with the storm of December 14-16, 1999

Heavy rainfall from the storm of December 14?16, 1999, triggered thousands of shallow landslides on steep slopes of the Sierra de Avila north of Caracas, Venezuela, and caused flooding and massive debris flows in the channels of major drainages that severely damaged coastal communities along the Caribbean Sea. Within this region we characterized geologic conditions where landslides initiated on hillsides and examined the texture of debris-flow deposits in the channels of nine drainages. In one of the most severely damaged areas on a highly developed alluvial fan at Caraballeda, we measured debris-flow deposits that ranged up to 5 meters (m) in thickness, inundating structures and roads over a large portion of the fan. Boulders up to 5 m long were carried along by the flows, impacted structures causing serious damage, and were deposited on the fan. Using field measurements and comparing pre-event and post-event topography from aerial photographs, we determined the volume of debris-flow and flood deposition on the fan to be about 2 million cubic meters. The total volume of material transported and deposited by landslides throughout the Vargas region ranks this as one of the most severe historical erosional events worldwide.

IMAP↗
USGS2001

Map Showing Susceptibility to Earthquake-Induced Landsliding, San Juan Metropolitan Area, Puerto Rico

Analysis of slope angle and rock type using a geographic information system indicates that about 68 percent of the San Juan metropolitan area has low to no susceptibility to earthquake-induced landslides. This is at least partly due to the fact that 45 percent of the San Juan metropolitan area is constructed on slopes of 3 degrees or less, which are too gentle for landslides to occur. The areas with the highest susceptibility to earthquake-induced landslides account for 6 percent of the surface area. Almost one-quarter (24 percent) of the San Juan metropolitan area is moderately susceptible to earthquake-induced landslides. These areas are mainly in the southern portions of the San Juan metropolitan area, where housing development pressures are currently high because of land availability and the esthetics of greenery and hillside views. The combination of new development and moderate earthquake-induced landslide susceptibility indicate that the southern portions of the San Juan metropolitan area are be at greatest risk.

Open-File Report↗
USGS2001

Continuous automated sensing of streamflow density as a surrogate for suspended-sediment concentration sampling

A newly refined technique for continuously and automatically sensing the density of a water-sediment mixture is being tested at a U.S. Geological Survey streamflow-gaging station in Puerto Rico. Originally developed to measure crude oil density, the double bubbler instrument measures fluid density by means of pressure transducers at two elevations in a vertical water column. By subtracting the density of water from the value measured for the density of the water-sediment mixture, the concentration of suspended sediment can be estimated. Preliminary tests of the double bubbler instrument show promise but are not yet conclusive.

Conference Paper↗
USGS2001

The rainfall-triggered landslide and flash-flood disaster in northern Venezuela, December 1999

Rainstorms in December 1999 induced thousands of landslides along the northern slopes of the Cordillera de la Costa mountain range principally in the state of Vargas, Venezuela . Rainfall accumulation of 293 millimeters during the first 2 weeks of December was followed by an additional 911 millimeters of rainfall on December 14 through 16. The landslides and floods inundated coastal communities resulting in a catastrophic death toll estimated at between 15,000 and 30,000 people. Debris flow damage to houses, buildings, and infrastructure in the narrow coastal zone was severe. Flash floods on alluvial fans at the mouths of rivers draining the coastal mountain range also contributed to the general destruction. In time scales spanning decades to centuries, the alluvial fans along this Caribbean coastline are areas of high geomorphic activity. Because most of the coastal zone in Vargas consists of steep mountain fronts that rise directly from the Caribbean Sea, the alluvial fans provide the only relatively flat areas upon which to build. Rebuilding and reoccupation of these areas requires careful determination of hazard zones to avoid future loss of life and property. A limited assessment of the distribution and character of landslides is currently in progress by the U.S. Geological Survey in cooperation with the Venezuelan Ministry of Environment and Natural Resources.

Conference Paper↗
USGS2001

Natural hazards on alluvial fans: the debris flow and flash flood disaster of December 1999, Vargas state, Venezuela

Large populations live on or near alluvial fans in locations such as Los Angeles, California, Salt Lake City, Utah, Denver, Colorado, and lesser known areas such as Sarno, Italy, and Vargas, Venezuela. Debris flows and flash floods occur episodically in these alluvial fan environments, and place many communities at high risk during intense and prolonged rainfall. In December 1999, rainstorms induced thousands of landslides along the Cordillera de la Costa, Vargas, Venezuela. Rainfall accumulation of 293 mm during the first 2 weeks of December was followed by an additional 911 mm of rainfall on December 14 through 16. Debris flows and floods inundated coastal communities resulting in a catastrophic death toll of as many as 30,000 people. Flash floods and debris flows caused severe property destruction on alluvial fans at the mouths of the coastal mountain drainage network. In time scales spanning thousands of years, the alluvial fans along this Caribbean coastline are dynamic zones of high geomorphic activity. Because most of the coastal zone in Vargas consists of steep mountain fronts that rise abruptly from the Caribbean Sea, the alluvial fans provide practically the only flat areas upon which to build. Rebuilding and reoccupation of these areas requires careful determination of hazard zones to avoid future loss of life and property. KEY TERMS: Debris flows, flash floods, alluvial fans, natural hazards, landslides, Venezuela

Conference Paper↗
USGS1995

Denudation rates determined from the accumulation of in situ-produced 10Be in the luquillo experimental forest, Puerto Rico

We present a simple method for estimation of long-term mean denudation rates using in situ-produced cosmogenic 10Be in fluvial sediments. Procedures are discussed to account for the effects of soil bioturbation, mass wasting and attenuation of cosmic rays by biomass and by local topography. Our analyses of 10Be in quartz from bedrock outcrops, soils, mass-wasting sites and riverine sediment from the Icacos River basin in the Luquillo Experimental Forest, Puerto Rico, are used to characterize denudation for major landform elements in that basin. The 10Be concentration of a discharge-weighted average of size classes of river sediment corresponds to a long-term average denudation of ≈ 43 m Ma −1, consistent with mass balance results.

Earth and Planetary Science Letters↗
USGS1995

Comparison of flank margin cave development on San Salvador island, Bahamas, and Isla de Mona, Puerto Rico

San Salvador Island, Bahamas is a 161 Km2 tectonically stable late Quaternary carbonate island located 600 km east-southeast of Miami FL. San Salvador contains numerous flank margin caves (phreatic karst features) that developed primarily in late Pleistocene eolianites. These caves developed during a short time in versy small fresh-water lenses. Cave elevations and Uranium-series ages from stalagmites indicate that all currently subaerial flank margin caves developed during the last interglacial seal-level highstand that was 6 m above current mean seal level 125,000 years ago (oxygen isotope substage 5e), which lasted no more than 14,000 years. The caves were formed by dissolution in the mixing zone at the margin of a freshwater lens that was elevated by the substage 5e highstand, and which resided within the small emergent portions of eolianite ridges. The flank margin caves have chambers with volumes greater than 1000 m3 on San Salvador; on other Bahamian islands, chambers as large as 14,000 m3 are known. Isla de Mona is 55km2, uplifted Late Miiocene-Pleistocene carbonate platform located in the Mona Passage 60 km west of Puerto Rico. Most of the island has 40 to 80 m high vertical cliffs to the sea which contain numerous flank margin caves at various elevations. A few cave chambers have volumes in excess of 100,000 m3. Paleomagnetic reversals observed in cave deposits and speleothems indicate the caves are at lease 780,000 years old as pre-Pleistocene. This age indicates that the caves may have developed in a stable, freshwater lens prior to Pleistocene glacio-eustasy, and have been subsequently tectonically elevated to their current position. The great size of the flank margin caves indicate mixing-zone dissolution in a large freshwater lens over an extended period of time. Flank margin caves in Isla de Mona, and some in the Bahamas contain evidence of two cycles of dissolution, in that speleothems and the cave wall rock to which they are attached show evidence on contemporaneous phreatic dissolution. In the Bahamas, the cause is most likely a minor change in sea level during the last interglacial highstand which caused a brief period of emergence, during which the subaerial speleothems grew, followed by re-submergence and dissolution. On Isla de Monta either tectonic motion, or the onset of glacio-eustasy, created the conditions that caused renewed phreatic dissolution after a period of subaerial exposure and speleothem precipitation. Despite differences in rock age and geologic setting, both San Salvador and Isla do Mona show evidence of re-invasion of the flank margin caves by dissolutionally aggressive water following a vadose interval. The flank margin caves have very similar morphologies and characteristics, and the only major difference is attrutable to the larger lens size and the longer duration of stable lens position on Isla de Mona. The data indicate that dissolution occurs rapidly in these environments, and despite the development of large voids, the same geochemical environment can be re-established after an emergence episode.

Conference Paper↗
USGS1993

Rainfall-threshold conditions for landslides in a humid-tropical system

Landslides are triggered by factors such as heavy rainfall, seismic activity, and construction on hillslopes. The leading cause of landslides in Puerto Rico is intense and/or prolonged rainfall. A rainfall threshold for rainfall-triggered landsliding is delimited by 256 storms that occurred between 1959 and 1991 in the central mountains of Puerto Rico, where mean annual rainfall is close to or in excess of 2,000 mm. Forty one of the 256 storms produced intense and/or prolonged rainfall that resulted in tens to hundreds of landslides. A threshold fitted to the lower boundary of the field defined by landslide-triggering storms is expressed as I = 91.46 D -0.82 where I is rainfall intensity in millimeters per hour, and D is duration in hours. Landslide-producing storms occurred at an average rate of 1.2 per year. In general the landslides triggered by short-duration, high-intensity rainfall events were mainly shallow soil slips and debris flows, while the long-duration, low-intensity rainfall produced larger, deeper debris avalanches and slumps. For storms that had durations of up to 10 h, landsliding did not occur until rainfall intensity was as much as three times as high as the rainfall intensity reported as sufficient to trigger landsliding in temperate regions. As storm durations approach 100 h, the rainfall conditions necessary to initiate landsliding in Puerto Rico converge with those defined for temperate regions. A comparison of the Puerto Rico threshold with rainfall data from other humid-tropical regions suggests that the threshold developed for Puerto Rico may be applicable to other similar environments throughout the world.

Geografiska Annaler, Series A: Physical Geography↗
USGS1992

Landslides triggered by Hurricane Hugo in eastern Puerto Rico, September 1989

On the morning of September 18, 1989, a category-four hurricane struck eastern Puerto Rico with a sustained wind speed in excess of 46 m/s. The 24-h rainfall accumulation from the hurricane ranged from 100 to 339 mm. Average rainfall intensities ranging from 34 to 39 mm/h were calculated for 4 and 6 h periods, respectively, at a rain gage equipped with satellite telemetry, and at an observer station. The hurricane rainfall triggered more than 400 landslides in the steeply sloping, highly dissected mountains of eastern Puerto Rico. Of these landslides, 285 were mapped from aerial photography which covered 6474 ha. Many of the mapped landslides were on northeast- and northwest-facing slopes at the eastern terminus of the mountains, nearest the hurricane path. The surface area of individual landslides ranged from 18 m2 to 4500 m2, with a median size of 148 m2. The 285 landslides disturbed 0.11% of the land surface in the area covered by aerial photographs. An approximate denudation rate of 164 mm/1000 y was calculated from the volume of material eroded by landsliding and the 10-y rainfall recurrence interval.

Caribbean Journal of Science↗
USGS1991

Physical aspects of Hurricane Hugo in Puerto Rico

On 18 September 1989 the western part of Hurricane Hugo crossed eastern Puerto Rico and the Luquillo Experimental Forest (LEF). Storm-facing slopes on the northeastern part of the island that were within 15 km of the eye and received greater than 200 mm of rain were most affected by the storm. In the LEF and nearby area, recurrence intervals associated with Hurricane Hugo were 50 yr for wind velocity, 10 to 31 yr for stream discharge, and 5 yr for rainfall intensity. To compare the magnitudes of the six hurricanes to pass over Puerto Rico since 1899, 3 indices were developed using the standardized values of the product of: the maximum sustained wind speed at San Juan squared and storm duration; the square of the product of the maximum sustained wind velocity at San Juan and the ratio of the distance between the hurricane eye and San Juan to the distance between the eye and percentage of average annual rainfall delivered by the storm. Based on these indices, Hurricane Hugo was of moderate intensity. However, because of the path of Hurricane Hugo, only one of these six storms (the 1932 storm) caused more damage to the LEF than Hurricane Hugo. Hurricanes of Hugo's magnitude are estimated to pass over the LEF once every 50-60 yr, on average.

Biotropica↗
USGS1990

Landslide processes in saprolitic soils of a tropical rain forest, Puerto Rico

Shallow soil slips, earth and debris slides appear to be a primary mechanism of hillslope denudation in the rainforest of eastern Puerto Rico. Annual rainfall in excess of 4,000 mm, and thick sequences (up to 20 m) of residual soils (saprolite) combine to produce these landslides. Shear strength testing and observatons of tension cracks indicate that landslides may start as tensile failure of saprolitic material. The tension cracks provide avenues for rapid infiltration of rainwater and saturation of the underlying soil. During or shortly after intense or prolonged precipitation, shear failure then occurs as a result of pore-pressure buildup along zones of low permeability within the saprolite. Tensile stresses in the unsaturated, low-density upper saprolite zone range from 3 to 10 kPa, and mean seismic refraction velocities are 476 +/- 127 m/s. Denser, clay-rich, less permeable saprolitic zones having mean seismic velocities of 1420 +/- 157 m/s represent zones that are commonly associated with perched ground water and are zones where exess pore-water pressure is most likely to trigger movement. These zones of translocated clay show marked density increases. Slickensides are present in the saprolite along relict fractures and joints derived from the parent rock; they are common in quartz-diorite bedrock, and less so in marine-deposited volcaniclastic bedrock. The failure planes of many landslides have exposed these relict fractures and joints as slickensides, and landslides appear to move on these pre-existing planes of weakness in the saprolite. The larges landslides (areas greater than 20,000 m 2 , however, are those that fail along saprolite-bedrock boundaries, which are zones of contrasting density and permeability within or at the base of the weathered profile.

Conference Paper↗