Photographs showing the effects of Hurricane Hugo in the Luquillo WEBB study area

Trees snapped by Hurricane Hugo winds, Luquillo Experimental Forest, 1989.

Hurricane Hugo struck eastern Puerto Rico on September 18, 1989 with maximum sustained winds of 166 km/h, with gusts of 194 km/h. Hurricane-force winds lasted about 4 h and the average time interval between occurrences (recurrence interval) of 166 km/h sustained winds was estimated at 50 years (Scatena and Larsen, 1991).

Small debris flow scar (~5 m wide) triggered by rainfall associated with Hurricane Hugo, Bisley Experimental Watershed, Luquillo Experimental Forest, 1989.

More than 400 landslides (mainly debris flows and shallow soil slips) were mapped from aerial photographs and field reconnaissance after the hurricane. Rainfall accumulation in the mapped area ranged from 200 to 300 mm and average rainfall intensity was 34 to 39 mm/h (Larsen and Torres Sánchez, 1992).

Aerial view of debris avalanche scars near PR Highway 191, Luquillo mountains, 1989.

The scar visible in the right center of the photograph (labeled with letter A) measures 153 m long, 23 to 33 m wide, and 3 to 10 m deep. It moved approximately 30,000 m³ of soil and rock downslope 3 days after Hurricane Hugo passed the island(Larsen and Torres Sánchez, 1996). The debris avalanche scar (identified with the letter B) measures 600 m from the ridge top to the 2-lane, vegetation-covered highway visible in the foreground. The highway (PR 191) has been closed since 1970 because of damage caused by these and several other debris avalanches.

Forest damage, Bisley Experimental Watershed, Luquillo Experimental Forest, Puerto Rico, 1989.

Defoliation, uprooting, and breakage of trunks were common effects of Hurricane Hugo on Luquillo Experimental Forest hillslopes. Because the hurricane track passed the northeast corner of the island, the strongest winds were mainly northerly and some of the greatest damage was noted on north-facing slopes. Note person in center of photograph for scale.

Aerial view of the Luquillo Mountains, Puerto Rico, 1989, looking towards the west.

During much of the 3 month period following Hurricane Hugo, the cloud base over the Luquillo Mountains was not at the usual 500-600 m level but was at an elevation of 900-1,000 m. The rise in cloud base apparently resulted from the increased temperature and albedo in defoliated areas (Scatena and Larsen, 1991). The highest peak visible in this photograph has an elevation of 1,074 m. Photograph taken 2 weeks after the hurricane.

Aerial view showing hurricane wind effects on ridge top near San Lorenzo, Puerto Rico, 1989.

The strong control exerted by topography is apparent in this photograph, taken two weeks after the passage of Hurricane Hugo. The defoliated hillslope on the right side of the photograph faces north. Northern-hemisphere hurricanes rotate in a counter-clockwise direction. Because Hurricane Hugo passed the northeast corner of Puerto Rico, north-facing hillslopes were exposed to the greatest wind velocities. (Debris-flow scar visible in lower right corner of photograph near home site is ~15 m long).

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