Vietnam

Introduction

The Vietnamese coastline extends for about 3,400 km, and includes two large river deltas, the Mekong Delta in the south and the Song Hong (Red River) Delta in the north, formed of Holocene alluvial deposits. Much of the intervening coast is backed by a narrow plain and mountain ranges, with ridges and valleys following structures along two main tectonic axes, a dominant SE–NW axis and a subordinate SW–NE axis. The main folding and faulting lines have also influenced the general outline of the coast. A basement of pre-Cambrian and early Palaeozoic granites, gneiss, rhyolite, porphyrites, and schists dominates the southern highlands, partly overlain by Mesozoic formations. North from Da Nang there are a series of SE–NW folds and faults in Palaeozoic and Mesozoic rocks.

The major mountain range of Vietnam, the Annamite Mountains, lies close to the coast, behind a coastal plain 30–50 km wide. This range forms the watershed between short rivers that flow eastward into the South...