Figure 2.8. Atlantic slope of the Continental Divide in the Monteverde Cloud Forest Preserve.
Photograph by Stephen Ingram.Below the cliff outcrops of the uppermost Aguacate
Group, the terrain of the Cordillera is highly dissected
into a landscape of small, narrow catchments sepa-
rated by ridges with steep flanks, often scored by land-
slides. Relief over small watersheds (10-15 ha) is typi-
cally >100 m. In some areas, such as the uppermost
San Luis and Penas Blancas valleys, extensive depos-
its of colluvial debris derived from landslides on both
the Aguacate Group and Monteverde Formation have
produced areas of less rugged relief.
2.3.1. Geomorphological Processes and
Distinctive Terrain Features
Rates of geomorphological activity, particularly denu-
dation due to mass wasting, have influenced land-
scape development at Monteverde and are central to
the concept of site stability (sensu Raup 1957). Ero-
sion of the deforested Pacific slope of the Cordillera
is of practical importance. The Cordillera itself has not
been the subject of quantitative geomorphological
study, but research in similar locales provides insight.
In volcanic ranges in central and southwestern Japan,
which are similar to the Cordillera de Tilaran in ele-
vation, relief, and precipitation depth (although some
of the precipitation is in the form of snow), sedimen-
tation rates in small reservoirs have been monitored
(Yoshikawa et al. 1981). Sedimentation rates yield
average rates of denudation of between 1000 and
10,000 m^3 /km^2 -yr (Yoshikawa 1974, Yoshikawa et al.
1981), equivalent to 1-10 mm/yr, which are commen-
surate with modern rates of uplift on the Osa and
Nicoya Peninsulas.
Exposed slopes often produce repeated landslides;
they supply debris for fluvial transport for long peri-
ods following the initial collapse. Landslides typically
occur episodically within an area, with a mean re-
currence interval of about 10 years (Yoshikawa et al.
1981). Sediment yield in a northern Californian water-
shed has also been shown to be strongly episodic; the
bulk of long-term sediment yield typically occurs in
the few years following widespread mass wasting as
a consequence of torrential rains (Dietrich et al. 1982a).
Distinctive terrain features ranging from small
permanent pools and swamps to cliffs, waterfalls,
quebradas, ridges, and landslides are conspicuous in
the Cordillera de Tilaran, although little is known
about their formation. These contribute markedly to
landscape and microclimate diversity. Geomorpho-
logical processes related to stream incision and slope
denudation (notably mass wasting) influence local
site stability.Swa m pS. Small (0.01-1 ha) swampy areas occur along
flat ridgetops and summits on the Continental Divide
and on the divide between the Penas Blancas and
Caiio Negro watersheds. These form because of high
wind-driven cloud water and precipitation inputs,23 The Physical Environment