Tropical karst of Vietnam - The main karstic region of Vietnam cover a total surface of 50,000 km2 and are to be found almost exclusively in North Vietnam, that is to say in 1/5 of the territory. They are situated in the distinct zone conditioned by the Tertiary and Quaternary phases. The largest zones are situated in the Northern and Eastern parts of the country. The least karstified zone is the West and southwest of Hanoi. The flooded coastal region (Isle of Catba, Along Bay) belongs to the boarder of the subsidence zone of the Red River delta. Although the damp tropical monsoon climate has varied very little from the Neogene until today, the karstic landscapes and degrees of evolution differ in each area and can range from cone, pyramid, tower to pinnacle karsts.