The Unique Tepuis
The smooth terrain that prevails in much of southeastern
Venezuela, part of the geologically ancient Guiana
Shield, is sharply punctuated by about 100 scattered,
flat- topped mountains called tepuis (plate 12- 4) that
together occupy an area of about 500,000 km^2 (200,000
mi^2 ). Tepuis are not part of the Andes, but are much older.
Were they located in the United States, tepuis would be
called mesas or table mountains, in reference to their
characteristic flattened summits. The word tepui, taken
from the Peñon Indian language, means mountain.
Rising abruptly from the flattened lowlands of the Gran
Sabana and its surrounding tropical rain forests, tepuis rise
from their forest- enshrouded bases as vertically steep,
rocky escarpments to heights of over 1,500 m (5,000 ft).
The tallest, Mt. Roraima, is 2,810 m (9,220 ft). The tepui
region, located approximately 650 km (400 mi) south of
the coastal city of Caracas, is home to the world’s highest
waterfall, Angel Falls, which plummets 979 m (3,212 ft)
from atop Auyan- tepui. Angel Falls (named for the bush
pilot Jimmy Angel, who “discovered” it in 1935), is one
of hundreds of waterfalls spilling from various tepuis,
continuing the ancient process of erosion.Tepuis are of interest not only for their obvious stark
beauty but also for their intriguing geological history.
They are ancient and eroded. If one could project oneself
back through time, to somewhere between 400 and
250 million years ago, the tepui region would be in close
proximity to what would eventually become the division
between South America and Africa, an area of lowlands
in proximity to the sea. Between 180 and 70 million years
ago, during the Mesozoic era, when dinosaurs were
abundant, the future tepui region began to take shape
as tectonic activity was separating the continents. At this
time the Andes were being uplifted to the west and the
Roraima Plateau was being eroded by a combination
of tectonic and meteorological activity. Evidence for
continental drift is seen in the sandstone of the tepuis,virtually identical to that found in the mountains of
the western Sahara. Erosion continued throughout the
Cenozoic era and the flattened tops of today’s tepuis are
all that remains of the once extensive Roraima Plateau.
Most of the mass of sandstone that once composed
the plateau has long since found its way to the oceans
through the continuous process of erosion. Today’s tepuis
represent but a fraction of that sandstone.The flattened, eroded tops of the tepuis represent
“sky islands,” an archipelago of isolated mountaintops.
Receiving as much as 400 cm (157 in) of rain annually,
much of it in the form of deluges from thunderstorms,
the plants and animals that tenant each tepui have
evolved essentially in isolation from populations in the
surrounding lowlands and, for that matter, on other
tepuis. Sir Arthur Conan Doyle was so inspired by the
splendid isolation of the wet, cloud- enshrouded tepuis
that he chose the region as the setting for his 1912
science- fiction novel The Lost World, about a land where
dinosaurs could still be found. No dinosaurs have as yet
been located on any of the tepuis, nor are they likely to
be, but the biota is nonetheless of great interest.
At least half of the tepuis’ approximately 10,000 plant
species are endemic, a clear example of the effect of
evolution on isolated populations. Orchids abound, with
61 species found on Auyan- tepui alone. Also common
are various plants that consume insects, such as pitcher
plants and sundews. The soil atop the tepuis is poor,
mostly eroded rock. Insectivorous plants are advantaged
in such a soil- impoverished habitat, because they can
supply their need for such nutrients as nitrogen and
phosphorus by digesting insect bodies.If you want to visit a tepui you are more or less out of
luck. I know of no tours that will drop you atop one. It
is, however, possible to arrange a flight that will take
you very close to them, in range of outstanding views of
Angel Falls.Plate 12- 4. The “sky islands” in the distance are tepuis, ancient table mountains of Venezuela. Photo by John Kricher.206 chapter 12 cruising the rivers to the sea