Geology
Why these tsingy are red, and why they will not last
A short account of iron oxide, runoff and a landscape that is younger than most of the villages around it.
Fetra Rasoanaivo
Geologist, University of Antsiranana
· 5 min read
Ask most visitors what tsingy are and they will describe Bemaraha: grey limestone blades, razor-edged, hundreds of metres deep. The Red Tsingy is a different phenomenon that happens to share a name.
Three ingredients
The Sahafary plateau is built from Isalo-series sandstone, marl and a thick laterite crust. Laterite is what tropical weathering leaves behind: quartz sand, kaolinite clay, and iron oxide. The iron is the pigment.
One process
Water does the rest. Runoff concentrates into gullies, gullies deepen into a canyon, and the softer beds erode faster than the harder ones. What is left standing are the columns, capped by the beds that resist.
Nothing here is cemented. These formations are held together by compaction and habit.
The timescale
The canyon is old. The individual pinnacles are not. Deforestation of the plateau accelerated erosion through the twentieth century, and the shapes visible today are largely decades old, not millennia.
What that means for you
It means the site is fragile in a literal sense: a hand on a column removes material that will not come back. It also means that if you visited five years ago and come again, you are not looking at the same place.
