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Madagascar PHYSICAL ENVIRONMENT
Topography
Madagascar - Unavailable
Figure 3. Madagascar: Topography and Drainage
Madagascar can be divided into five geographical
regions: the
east coast, the Tsaratanana Massif, the central highlands,
the
west coast, and the southwest. The highest elevations
parallel
the east coast, whereas the land slopes more gradually to
the
west coast
(see Madagascar -
fig. 3).
The east coast consists of a narrow band of lowlands,
about
fifty kilometers wide, formed from the sedimentation of
alluvial
soils, and an intermediate zone, composed of steep bluffs
alternating with ravines bordering an escarpment of about
500
meters in elevation, which gives access to the central
highlands.
The coastal region extends roughly from north of Baie
d'Antongil,
the most prominent feature on the east coast of the island
formed
by the Masoala Peninsula, to the far south of the island.
The
coastline is straight, with the exception of the bay,
offering
less in the way of natural harbors than the west coast.
The Canal
des Pangalanes (Lakandranon' Ampalangalana), an
800-kilometerlong lagoon formed naturally by the washing of sand up on
the
island by the Indian Ocean currents and by the silting of
rivers,
is a feature of the coast; it has been used both as a
means of
transportation up and down the coast and as a fishing
area. The
beach slopes steeply into deep water. The east coast is
considered dangerous for swimmers and sailors because of
the
large number of sharks that frequent the shoreline.
The Tsaratanana Massif region at the north end of the
island
contains, at 2,880 meters, the highest point on the island
and,
north of this, the Montagne d'Ambre (Ambohitra), which is
of
volcanic origin. The coastline is deeply indented; two
prominent
features are the excellent natural harbor at Antsiranana
(Diégo
Suarez), just south of the Cap d'Ambre (Tanjon' i
Bobaomby), and
the large island of Nosy-Be to the west. The mountainous
topography to the south, however, limits the potential of
the
port at Antsiranana by impeding the flow of traffic from
other
parts of the island.
The central highlands, which range from 800 to 1,800
meters
in altitude, contain a wide variety of topographies:
rounded and
eroded hills, massive granite outcrops, extinct volcanoes,
eroded
peneplains, and alluvial plains and marshes, which have
been
converted into irrigated rice fields. The central
highlands
extend from the Tsaratanana Massif in the north to the
Ivakoany
Massif in the south. They are defined rather clearly by
the
escarpments along the east coast, and they slope gently to
the
west coast. The central highlands include the Anjafy High
Plateaux; the volcanic formations of Itasy (Lake Itasy
itself is
found in a volcanic crater) and the Ankaratra Massif,
reaching a
height of 2,666 meters; and the Ivakoany Massif in the
south. The
Isalo Roiniforme Massif lies between the central highlands
and
the west coast. Antananarivo, the national capital, is
located in
the northern portion of the central highlands at 1,468
meters
above sea level. A prominent feature of the central
highlands is
a rift valley running north to south, located east of
Antananarivo and including Lac Alaotra, the largest body
of water
on the island, having a length of forty kilometers. The
lake is
located 761 meters above sea level and is bordered by two
cliffs,
rising 701 meters to the west and 488 meters to the east,
which
form the walls of a valley resembling the rift valleys of
East
Africa. This region has experienced geological subsidence,
and
earth tremors are frequent here.
The west coast, composed of sedimentary formations
deposited
in several layers over time, is more indented than the
east
coast, especially in the northwest, thus offering a number
of
fine harbors sheltered from cyclones, such as the harbor
at
Mahajanga. Deep bays and well-protected harbors have
attracted
explorers, traders, and pirates from Europe, Africa, and
the
Middle East since ancient times; thus, the area has served
as an
important bridge between Madagascar and the outside world.
Yet
the broad alluvial plains found on the coast between
Mahajanga
and Toliara, which are believed to have great agricultural
potential, are thinly inhabited and remain largely
unexploited.
The southwest is bordered on the east by the Ivakoany
Massif
and on the north by the Isala Roiniforme Massif. It
includes two
regions along the south coast, the Mahafaly Plateau and
the
desert region occupied by the Antandroy people.
The Mananara and Mangoro rivers flow from the central
highlands to the east coast, as does the Maningory, which
flows
from Lake Alaotra. Other rivers flowing east into the
Indian
Ocean include the Bemarivo, the Ivondro, and the
Mananjary. These
rivers tend to be short because the watershed is located
close to
the east coast. Owing to the steep elevations, they flow
rapidly,
often over spectacular waterfalls. The rivers flowing to
the west
coast and emptying into the Mozambique Channel tend to be
longer
and slower, because of the more gradual slope of the land.
The
major rivers on the west coast are the Sambirano, the
Mahajamba,
the Betsiboka (the port of Mahajanga is located at the
mouth),
the Mania, the North and South Mahavavy, the Mangoky, and
the
Onilahy. The Ikopa, which flows past Antananarivo, is a
tributary
of the Betsiboka. The Mangoky River has a basin area of
some
50,000 square kilometers; the Ikopa River and the
Betsiboka River
have basin areas of 18,550 and 11,800 square kilometers,
respectively. The principal river in the south, the
Mandrare, has
a basin area of some 12,435 square kilometers, but it runs
dry
during certain months in this desert region. Important
lakes,
aside from Alaotra, include Lake Kinkony in the northwest
and
Lake Ihotry in the southwest.
Madagascar has been called the "Great Red Island"
because of
the supposed preponderance of red lateritic soils. The red
soils
predominate in the central highlands, although there are
much
richer soils in the regions of former volcanic
activity--Itasy
and Ankaratra, and Tsaratamana to the north. A narrow band
of
alluvial soils is found all along the east coast and at
the
mouths of the major rivers on the west coast; clay, sand,
and
limestone mixtures are found in the west; and shallow or
skeletal
laterite and limestone are located in the south.
Data as of August 1994
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