the larger slides that are conspicuous on quebrada
walls and the flanks of ridges produce one of the major
vegetation patterns in the Cordillera, which is a mo-
saic of forests of various ages. This mosaic indicates
that landslides are a natural feature in the Cordillera,
much like those on volcanic terrain in Hawaii (Went-
worth 1943, White 1949; Fig. 2.9).
Landslides consist of a zone of removal in the upper
portions, where more resistant materials are exposed,
and a zone of deposition at the bottom, where debris
accumulates. In the upper zone, patches of undisturbed
or slightly disturbed soil and vegetation may exist on
the slide periphery or as islandlike areas within the
main body of the slide, amid areas of exposed subsoil
and outcrops of bedrock. The lower zone may contain
areas where soil and rocks are piled at their angle of
repose, or areas where shattered trees are jumbled amid
rocks and boulders in giant precarious tangles. Land-
slides longer than 25-30 m may disintegrate into de-
bris avalanches or, if the water and soil content is high,
into debris flows. Many landslides dump debris into
stream channels at the bottom of quebradas. Seepage
may selectively remove fine-grained soil particles
and leave cobbles and boulders. Under these circum-
stances, stony hummocks comprise the floor of the
upper bowl of the valley adjacent to the headwall. In
other circumstances, the basal zone is rapidly eroded
directly by the stream, and the region of rapid reveg-
etation at the base of the slide is significantly reduced.
Large landslides may temporarily dam the stream, until
the impounded water breaks the dam and flushes the
debris downstream.
Not all portions of the landscape are at equal risk
of landslides. In the Cordillera, large slides are most
conspicuous on precipitous slopes where rocks of
the upper Aguacate Group are exposed. These sites
include the headwall of the Pefias Blancas valley,
Quebrada Honda, and the gorge of the Rio Guacimal.
Although landslides are typically more abundant on
steeper slopes (Wentworth 1943, White 1949, Swanston
1974, Jibson 1989), geological substrate (Day 1980,
Jibson 1989, Gupta and Joshi 1990), soil developmentFigure 2.9. A recovering landslide on the
slopes of the Monteverde Cloud Forest
Preserve. Photograph by Robert 0. Lawton.25 The Physical Environment