Last update: December 5th, 2019 at 8:00 am
An astronaut took this photograph of muddy floodwaters and distributary channels in the northern sector of the Tsiribihina River delta on Madagascar’s west coast. It was taken in April 2015 from the International Space Station.
Delta distributaries (channels and streams) have two morphologies: large and relatively straight or small and highly contorted. In the photo, brown sediment has been stirred up by heavy rains; when it reaches the sea, it is swept north (to the left in this image) by local ocean currents. Clearer blue water is visible to the lower right (south).
Over thousands of years, the sediment supplied by the river has been shaped by waves into beach ridges along the shoreline. Those ridges appear as many parallel lines, with each line representing a prior coastline on this fast-changing (geologically speaking) coast. The oldest coastline lies furthest inland.
Four cyclones hit Madagascar in the first four months of 2015. Heavy floods followed a mid-January storm and affected not only the 50 kilometer (31 mile) shoreline of the delta but also the lower 75 kilometers (47 miles) of the river.