Travel Reference
In-Depth Information
Significant
landscapeevolution
has occurred over the last 40 million years. Since India
began to head northeast, the rift between Africa and Madagascar stabilised and mountains
were regenerated by activity on major NNE- and NNW-oriented faults. These orientations
can be recognised across the country bounding smaller sedimentary basins and mountain
ranges, and most noticeably control the strikingly linear geometry of the east coast. The
centre and east were uplifted more than the west, providing the basis for the modern shape
oftheisland.Completelyemergentforthefirsttimeforseveralhundredmillionyears,land
plants and animals proliferated and evolved towards the island's present flora and fauna.
Locallakeandriverdepositsdevelopedinthelowlandsanderosioncutbackthehighlands.
In the centre and east, the entire marine record was stripped away, revealing the crystalline
core and resulting in undulating dome-like mountains, such as Pic d'Imarivolanitra. In the
westthesedimentaryrockwaserodedflattonearsealevel.Tectonicactivityinthelastmil-
lion years has again uplifted the Malagasy terrain, and this ancient erosional surface now
defines the plateaux of the west, including Bemaraha.
HUMAN COLONISATION
The final chapter starts just 2,000 years ago, when skilled
Malay boatmen found their way to then-uninhabited Madagascar and began a dramatic
demonstration ofhowhumans can affect geological processes. Reduction in primary forest
since the colonisation of Madagascar has indisputably influenced the shape of the land.
Soils once stabilised by deep root systems became susceptible to erosion, and the sediment
load in the rivers increased. In the 50 years to 1945, 40m of clay was deposited in the delta
oftheBetsiboka RiveratMahajanga, immensely morethantheunderlyingsedimentary re-
cord suggests was usual prior to deforestation. Ubiquitous hillside scars (called
lavaka
) are
the inland testimony to this accelerated redistribution of material from highlands to coast,
an inexorable environmental response to deforestation that is sending the Malagasy high-
lands towards eventual peneplanation (flattening) at an incredible rate. Even with an aver-
age annual erosion of 1mm taking place continuously, Madagascar will be reduced to near
sea level in a geologically short three million years.
FLORA
Madagascar and its adjacent islands harbour some 13,000 species of flowering plants of
which a staggering 89% are endemic. Although some other regions of the world (such as
the Tropical Andes, Indonesia and Brazil) have more plant species, they have substantially
lowerratesofendemism,typicallybelow50%.Madagascaristheworld'snumberoneflor-
al hotspot for an area its size. The fortuitous break from Africa and Asia at a time when
