The World Nature Heritage (the 2nd time) in geological and geomorphological value in Ha Long Bay, Vietnam
Halong bay is not only well-known for grandeur landscape admitted as the World Natural Heritage by UNESCO in 1994 (the 1st time) but also remarkable with geological and geomorphological value, especially krast geomorphology. These values are international and unique over the world.
The process of recognizing Halong bay as the World Natural Heritage by UNESCO for the second time in geology and geomorphology was carefully verified every steps. According to suggestion of Halong bay management board and IUCN (International Union for Conservation of Nature), professor Tony Waltham in geology, Trent Nottingham University, Britain came to Vietnam to research geology of krast limestone in Halong bay in September, 1998. After thorough research, he sent a geological and geomorphological record of Halong bay to UNESCO in Paris. No sooner had UNESCO received the record than it sent requirement to promote profiles of geological and geomorphological value in Halong bay to People’s Committee of Quang Ninh Province, Vietnam UNESCO Committee and Halong bay management board on 25th, February, 1999.
The profile submitting to the World Natural Heritage Council to recognize Halong bay as the World Natural Heritage in geological and geomorphological value was sent to the World Heritage center in Paris in July, 1999.
Professor Erery Hamilton Smith, IUCN came to Halong to verify the last time in March, 2000.
The 24th conference of the World Heritage Council in Cairns city, Queensland, Australia agreed on secondly recognizing Halong bay as the World Natural Heritage in geological and geomorphological value.
Geological and geomorphological values are evaluated by two criteria: tectonic history, karst geology and geomorphology.
Tectonic history of geology and geomorphology of Halong bay spent at least 500 years with very diferrent ancient circumstances of geography. After many times of mountain forming, regression, sinking and ingression… Halong bay has remained marks of the Earth’s great mountain and geosyncline forming which were constructed ancient horst and sunken block.
Halong bay used to be the deep ocean in Ordovic – Silur era (410-500 million years ago) and shallow sea in Cacbon-Pecmi (340-250 million years ago). In Tria era (240- 195 million years ago), while the Earth specially Europe had hot dry climate, Halong bay was a wet marsh with giant cycas and fern forest accumulated many generations.
Krast geomorphological value of Halong bay was created by fencong type (one of two typical karst topography types of Halong bay). Krast evolution of Halong expericed 20 million years by combination of thick limestone layer, hot and humid climate and fencong and fenglin krast topography types (geological formation).
Fengcong karst topography includes a cone-shaped limestone cluster in juxtaposition with around 100m high and the highest is 200m.
Fenglin is featured by separated peaks forming abrupt towers. Almost towers are 50-100m high. Height and width are in the ratio of 6m.
The complete karst process of Halong experienced 5 periods. The first one was an ancient plain or an inherited flat field. The second period was time of funnel-shaped karst topography. In the next period, pyramid and cone-shaped hills connected together. The fourth period developed abrupt high towers separated and finally it was period of karst plain.
Krast field is wide hollow-shaped, developing in krast areas with size similar to sinkhole, sunken block due to ceiling collapse of undergound river valleys, caves and insoluble stone layers powerfully eroded among higher karst…
Furthermore, Halong bay has underground krast. This is a diverse cave system divided into 3 main group:
The first group is ancient underground caves, especially caves such as Sung Sot, Tam Cung, Lau Dai, Thien Cung, Dau Go, Thien Long… Almost of these caves are drainages from karst funnels of ancient underground caves. Nowadays, these located in diferent high levels with slope paths and large tottery distances.
The second group is karst floor caves such as Trinh Nu, Bo Nau, Trong, Tien Ong. The ancient floor caves were formed during expansion of erosion and played role as a drainage from bigger underground cave systems inside limestone. These caves horizontally communicate with each other and often connect to stone abrasive benches or accumulated benches in base level.
The third group is vaulted entrance system exspecially 3 communicated caves such as Ho Ba Ham (Ba Ham Lake), Luon, Hang. This is typical feature of Halong. The dissolving process of limestone into sea water boosted by wave and tide created vaulted entrance system in sea. In convenient condition, vaulted entrances were deepened into small caves, even went through limestone mountains to form caves connected to sea lakes. These caves are featured by a horizontal roof which is pretty flat and cut across limestones. The caves were formed not only in current water level but also in fluctuating level in ingression period Holoxen, even in ancient water level Pleitoxen.
Besides, Halong geology also has Quaternary geological and coastal value, typically remarkable features of quaternary geology.
Quaternary sediment, surfaces of raised offshore bench and sunken subtage plain, ancient valley and river system in forms of narrow passages in the bottom of the bay, cave system, vaulted entrance system are clear evidences of Quaternary geological inventions.
Concerning about coastal geology, Halong bay is considered a modern accumulated place, formed from island system outside instead of small tips of mainland. The process of chemical shore erosion nourishing in akailine environment creates extensive vaulted entrance, making limestone island more strange.
Geological environment is platform to develop the other values of Halong such as biological diversity, archaeological culture and other humanistic values.