Geology and geomorphology of Son Doong Cave

Located in the core zone of Phong Nha Ke Bang National Park, Bo Trach District, Quang Binh Province, Son Doong Cave not only has great size but also contains special geological and geomorphological values.

Geological and geomorphological features

Geology of Son Doong Cave: The cave was formed inside the oldest limestone massif in Asia (400 – 450 million years old). Through the analysis of sediment samples, Son Doong had been defined as a young cave, from 2 to 3 million years old.

The cave was formed by erosion over millions of years by allogenic rivers, the Rao Thuong and Khe Ry (the longest river cave in Asia), sinking along a straight sub-vertical faultline of the Truong Son mountain range, and forming a giant tunnel underneath the limestone mountains. Thin limestone layers and large fault lines caused two roof collapses or skylights to form.

Doline 2 - Garden of Edam - A jungle inside the Son Doong Cave.

Son Doong Cave is divided into 3 sections: The first part, from the cave entrance to Doline 1, is still active with a permanent underground river. This section has many sediments indicating regular flooding during the wet season. The collapse at the first Doline acts as a dam causing the passage to fill up to the Level Playing Fields campsite.

The second and third sections of the cave are fossil passages and the Passchendaele, with no active rivers. This has allowed the development of extensive calcite formations in these passages. Passchendaele carries a small stream, and after heavy rainfall may fill up to form a lake, leading to the Wall of Vietnam, a huge calcite wall.

Two dolines have formed in the central section of the cave. The first is likely to be due to the collapse of some thin limestone layers, which cannot support the roof of such a high passage. The second doline is located at a junction of two fault lines, creating a weakness and resulting in collapse.

Fossil passages and Passchendaele passage.