THE OUTSTANDING VALUE OF THE GEOLOGY OF HA LONG BAY
Tran Duc Thanh(1) & Tony Waltham(2)
(1).Haiphong Institute of Oceanology; 246 Danang Street, Haiphong city, Vietnam;
(2). Nottingham Trent University, England
Nature has given Ha Long Bay many precious values. Ha Long bay was first
recognised as a World Natural Heritage Area solely on the basis of its outstanding landscape
value. The beauty and aesthetic value of natural landscape of the Bay reflect the shapes and
the colours of jewels. However, it is geological structure and material of the bay that have
created the jewels. The outstanding value of Ha Long Bay’s geology and geomorphology
needs to be conserved for the benefit of future generations. This paper is a preliminary review
of that value.
1.THE VALUE OF REGIONAL GEOLOGY
Ha Long Bay, the area near the shore and other area adjacent to the Bay are composed
of thick beds of limestone and clastic sediments which have been aged from ancient to the
present day. This is the carved picture of geological processes which occurred hundreds of
million of year ago. Throughout this time while the colour, the ingredients and the
architecture of the limestone beds were being formed, fossil relicts have been preserved
between the layers. These, and the nature of the sediments, contribute to a scientific record of
Mane sedimentary rocks contain remains and traces of flora and fauna of the ancient
past in many forms including those of plants and creatures that become extinct many years
ago. This leaves a store of information about the evolution and development of life on the
Earth (Table 1).
In the geological structure, Ha Long bay lies in the Duyen Hai Zone
(Dovjicov, A.E. et all, 1971) belonging to Caledonian-Katasia structure which suffered from
orogenic movement during the early Palaeozoic era. On the Caledonide folded basement, the
Indosinian orogeny at the end of Triassic period formed the block faults and bearing
anthracite sediments were deposited. The well-known sub-latitude deepening fault system of
Vietnam has developed in this zone (Can, N., et all, 1994) The series of the movement also
formed the Cua Luc and Ha Long depressions, which were subsequently flooded by sea. The
record of the old, recent movement are clearly shown in Ha Long Bay area in the strong
deformation of sedimentary layers such as gentle and returned folds, and normal and reverse
faults with the tectonic breccia belts. They are of Nature’s lively Sculptures preserved on the
limestone cliffs normally.
The Ha Long Bay has a long geological history with the different paleogeographical
environments commencing nearly 570 million years ago (Table 2). Between Ordovician and
Silurian periods (500 to 410 million years ago), the area was the deep sea. Latter, between
Carboniferous and Permian periods (340 to 250 million years ago), the area fell into the
sallow sae environment. By the end of Paleogenic and the beginning of Neogenic periods,
between 26 and 20 million years ago, the sea area had become part of a large coastal
peneplain. This was inundated by sea several times in the Quaternary, during 2 million last
years. The present Ha Long Bay was formed around 7 or 8 thousand years ago by the sea
invasion during Holocene transgression begun at about 17-18 thousand years ago (Thanh,
T.D. et all, 1997; Thanh, T. D., 1998).
The geological history of Ha Long bay involved three major periods of orogeny
(Thanh, T. Dz., 1977) . The first was Caledonide epi-geosynclinal orogeny at the end of
Silurian periods, about 410 million years ago. The second was Indosinide epi-platform
orogeny at the end of Triassic period, about 200 million years ago. The last Alpide orogeny
in the late Paleogene period, around 30 million years ago created the distinction between
horst mountains and graben depressions which was basis of the formation of Ha Long Bay
latter. There existed two distinguished paleogeographical environments in Ha Long Bay area.
The Carboniferous periods, between 340 and 285 million years ago, was a warm period all
over the planet when huge swamps created the great coal basins of Europe and America. In
Ha Long Bay, carbonate sediments were deposited in a shallow sea in dry, hot conditions,
gradually building in to thick beds of limestone. Throughout the hundred – million year
period, the sea bed gradually subsided thereby allowing the limestone under the shallow sea
to accumulate in thick layers eventually achieving a thickness of 1,200m eventually
permitting the formation of a characteristic karst landscape. By contrast, during the Triassic
period between 240 and 195 million tears ago when most of the rest of the world was
experiencing hot, dry climatic conditions, the Ha Long region had a hot, wet climate. The
decayed remains of enormous forests of tree ferns were the basis of coal deposits in the area.
The present Ha Long Bay is a karst plain that has been submerged by the sea and is
the result of a geological history spanning more a hundred million years. Prior to the
formation of Ha Long Bay, 300 to 240 million years ago, there must have been an ancient sea
above a 1000 m thick bed of limestone. The 20 million year process of karts erosion took
place during the Neogenic and Anthropogenic periods the much later marine invasion is
related to a warmer climate all over the planet over ten thousand years ago.
2. The Quaternary and the marine geological values
The Ha Long Bay area has many valuable features of the Quaternary period. The
Quaternary sediment players, the upper sea bed with a plain surface conserving ancient rivers,
systems of caves and deposits of sediments, traces of ancient marine action forming
distinctive notches are important evidence of geological events and processes taking place at a
time when human beings inhabited the earth. Particularly from the Holocene time, from about
11,000 years ago when modern, intelligent humans had developed, Ha Long Bay has much
archaeological evidence connecting variations in sea levels with the development of ancient
cultures such as the Soi Nhu and Ha Long cultures. Unfortunately, this aspect has not yet been
researches or evaluated in detail.
In terms of marine geology, Ha Long is recorded as a modern sedimentary basin, a
bay created by a system of boundary islands. The Bay has strong tidal currents, but weak
ware. In the alkaline environment, the chemical denudation process of calcium carbonate
proceeds rapidly, creating wide, strangely shaped marine notches. This appears to be an active
process, concerning CO2 supplied from respiration of algae and plants living in Ha Long Bay.
3. Karst geomorphic value
Ha Long Bay is a mature karst landscape developed during a warm, wet, tropical
climate. The sequence of stages in the evolution of a karst landscape over a period of 20
million years requires a combination of several distinct elements including a massive
thickness of limestone, a hot wet climate and slow overall tectonic up lift. Waltham. T. 1998
According to Chinese scientists, the process of karst formation is divided into five stage is the
formation of the distinctive do line karst. This is followed by the development of fengcong
karst can be seen in the groups of hills on Bo Hon and Dau Be Inland. These cones with
sloping side average 100m in height with the tallest exceeding 200m. Fenglin karst is
characterised by steep separate towers. The hundreds of rocky islands with form the beautiful
and famous landscape of the Bay are the individual towers of a classic Fenglin landscape
where the intervening plains have been submerged by the sea. Most towers reach a height of
between 50 and 100m with a height to width ratio of about 6. The karst dolines were flooded
by the sea becoming the abundance of lakes that lie within the limestone islands. For
example, Dau Be island at the mouth of the Bay has six enclosed lakes including those of the
Ba Ham lakes lying within its fencong karst. The Bay contains examples of the landscape
elements of fengcong, fenglin and karst plain. These are not separate evolutionary stages but
the result of natural non – uniform processes in the denudation of a large mass of limestone.
Marine erosion created the notches which in some places have been enlarged into caves. The
marine notch is a feature of limestone coastline but, in Ha Long Bay, it has created the mature
Table 1: The geological history of Ha Long Bay
HoloceneMarine transgression, after world's glaciations, overran
the coastal areas to form the modern Ha Long
Bay. This is mainly a land environment, with
development of karst landscapes and river
systems. Systems of caves formed at heights of
10-15 m, 20-30 m and 40-60 m.
A marine transgression formed the ancient Ha Long
Bay. Previously the sea-level had been 100-120 m
lower than today and well outside the modern coast
during the cold stages of the glacial Ages.
Tectonic downwarpings of Cua Luc Bay and Ha Long
Uplift tectonic movements on Dong Trieu Arc.
The East Sea is formed. River erosion and alluvial
deposition formed a large peneplain.
A continental environment with orogenic movements
Erosion processes are strong.
A land environment, where tectonic downwarping
created a coal swamp basin is followed by strong
movements of the Indosinian orogeny.
Downwarping disturbed the coastline creating a land environment.
A shallow warm sea enlarged from the west, rich in
sea creatures, including coral, foraminifera,
brachiopods and crinoids. Limestone, over a thousand
metres thick, is formed.
Ha Long Bay is a land area. Nearby the Quan Lan
archipelago, Trang Kenh, Do Son and Cat Ba were
downwarpings invaded by the sea.
Open sea with deep water in the Katazia geosyncline.
The sea extended to the west, but the East Sea
was a landmass.
Table 2. Sediment formations and fossils in Ha Long Bay and its surrounding areas
(Dovjicob, A. E. et all, 1971, Luong, N. C. et all, 1980 and Toan, N. Q. et all 1993)
Or Name of Sight ThickSediment FossilsGeological Location
der formation ness ingredients period
1 Cô Tô03 – S1ct
Con Ng a
D1 – 2dd
Raw clastic Coral,
V n C nh
3 L S n
Trà B n,
Đ S n
in Do Son
Quán L n,
Trà B n
5 Ph Hàn
6 Cát BàC1cb450Limestone Coral,
8 Bãi CháyP2bc
C a L c
C m Ph
10Đ ng Ho
C a L c
C a L c
12 Các H ệ
t ng Đ
Within Ha Long Bay, the main accessible caves are the older passages that survive
from the time when the karst was evolving though its various stages of fengcong and
fenglin. Three main types of caves can be recognized in the limestone islands (Waltham, T.
1- Remnants of old phreatic caves
2- Old karstic foot caves
3- Marine notch caves
The first group of caves is old phreatic caves which include Sung Sot, Tam Cung,
Lau Dai, Thien Cung, Dau Go, Hoang Long, Thien Long. Nowadays, these caves lie at
various high levels. Sung Sot cave is on Bo Hon island. From its truncated entrance
chambers on aledge high on the cliff, a passage of more that 10m high and wide descends
to the south. Tam Cung is a large phreatic fissure cave that developed in the bedding
planes of the limestone dividing the fissure cave into three chambers. Lau Dai is a cave
with a complex of passages extending over 300m opening on the south side of Con Ngua
island. Thien Cung and Dau Go are remnants of the same old cave system. They both
survive in the northern part of Dau Go island at between 20 and 50m above sea level.
Thien Cung has one large chamber more that 100m long, blocked at its ends and almost
subdivided into smaller chambers by massive wall of stalactites and stalagmites. Dau Go is
a single large tunnel descending along a major set of fractures to a massive choke.
The second group of caves is the old karstic foot caves which include Trinh Lu, Bo
Nau, Tien Ong and Trong caves. Foot caves are a ubiquitous feature of karst landscapes
which have reached a stage of widespread lateral undercutting at base level. They may
extend back into maze caves of stream caves draining from larger cave systems within the
limestone. They are distinguished by the main elements of their passages being close to the
horizontal and are commonly related to denuded or accumulated terraces at the old base
levels. Trinh Nu, which is one of the larger foot caves in Ha Long Bay with its ceiling at
about 12m above sea level and about 80m in length, was developed in multiple stages. Bo
Nau, a horizontal cave containing old stalactite deposits, cuts across the 25o dip of the
The third group is the marine notch caves that are a special feature of the karst of
Ha Long Bay. The dissolution process of sea water acting on the limestone and erosion by
wave action crates notches at the base of the cliffs. In advantageous conditions, dissolution
of the limestone allows the cliff notches to be steadily deepened and extended into caves.
Many of these at sea level extend right though the limestone hills into drowned dolines
which are now tidal lakes.
A distinguishing feature of marine notch caves is an absolutely smooth and
horizontal ceiling cut through the limestone. Some marine notch caves had been not
formed at present sea level, but old sea levels related to sea level changes in Holocene
transgression, event to Pleistocene sea levels. Some of them passed preserved the
development of old karstic foot cave in mainland environment or preserved the remnants
of older phreatic caves. One of the most unusual features of Ha Long Bay is the Bo Ham
lake group of hidden lakes and their connecting tunnel – notch caves in Dau Be island.
From the island’s perimeter cliff a cave, 10m wide at water level and curving so that it is
almost completely dark, extends about 150m to Lake 1. Luon cave is on Bo Hon island and
extends 50m though to an enclosed tidal lake. It has a massive stalactite hanging 2m down
and truncated at the modern tidal level. It has passed though many stages in its formation.
The karst landscape of Ha Long Bay is of international significance and of
fundamental importance to the science of geomorphology. The fenglin tower karst, which
is the type present in much of Ha Long Bay, is the most extreme form of limestone
landscape development. If these karst landscapes are broadly compared in terms of their
height, steepness and number of their limestone towers, Ha Long Bay is probably second
in the entire world only to Yangshou, in China. However, Ha Long Bay ha also been
invaded by the sea so that the geomorphology of its limestone is lands are, at least in part,
the consequence of marine erosion. The marine invasion distinguishes Ha Long Bay and
makes it unique in the world. There are other areas of submerged karst towers which were
invaded by the sea, but none is as extensive as Ha Long Bay.
4. Mineral resources and other values
The value of the mineral resources of Ha Long Bay cannot be ignored, although
their exploitation is another issue that needs to be considered in relation to conservation
and development. There is an enormous reserve of limestone in the Ha Long area,
hundreds of millions of tons with a calcium carbonate content of between 96% and 100%.
Conservation of this area also has to take into account the maintenance of this vast
carbonate. Limestone formations also have a solid black silica layers, important for art
material. The coal deposits of Hon Gai Basin are of high grade anthracite with a calorific
value of between 7000 and 8400 Kcal/kg, an ash content of between1.2% and 1.5% and a
sulfur content of between 0,2% and 1,2%.
The Tertiary sedimentary formations onshore of Ha Long Bay have a great reserve
of clay materials for bricks and tiles of which hundreds million have been manufactured a
year recently. Dong Ho formation with the stones bearing oil has been determined as
Oligocene age shows the petroleum prospect in coastal Northeast part of Vietnam ( Trung,
P.Q. et all, 1999).
The tourism development value of Ha Long Bay is increasingly determined by the
value of the geological resource factor. However, the attraction would be much greater
were the geological value to be more effectively. Apart from scientific tourism, if the
geological value is explained through effective interpretation and representation, tourism
gain not only an appreciation of the beauty of the natural landscape but also come to
understand the value of the heritage - its geological history, structure, process of creation
and so on.
As well as its close relation to the value of the natural landscape, the geology of Ha
Long Bay is associated with the value of the bio – diversity of the eco – systems, such as
the coral reefs and mangroves on and around the islands of Ha Long Bay. In some caves,
such as Sung Sot, Trinh Nu, Vung Ba Cua, Hoang Long, Dau Go and Bo Nau, there are
In many caves, archeologists have found remains and artefacts of the Soi Nhu
culture of the late Pleistocene period and the Ha Long culture of the middle Holocene
period. An old picture was also found on the roof of a cave on the west bank of Vung Ba
Cua island. Dau Go cave is regarded as the place where the wooden stakes for the battle at
the Bach Dang River in 1288 were hidden.
Ha Long Bay has outstanding values of geology and geomorphology. These include
the scientific values of regional geology, Quaternary geology, marine geology and karstic
geomorphology. In addition there are the resource values of minerals and tourism and the
ancillary values of archeology and bio – diversity. Of these, the value of the karstic
geomorphology is the most outstanding and unique, and plays a fundamental role in the
science of karstic geomorphology. In addition to its natural landscape value, Ha Long Bay
is worthy of further recognition as a World Heritage in respect of its geological value. The
conservation of this heritage is, therefore, of the highest level of importance.
1. Can N. et all. 1994. Recent faulting in Hai Phong – Quang Yen area. In: Marine
resources and environment. Sci and Tech. Pub. House. Ha Noi. p. 54 - 60.
2. Dovjicov, A. E; N. v. Chien at all, 1971. Geology of North Viet Nam. Sci and Tech.
Pub. House. Ha Noi.
3. Luong N. C, et all 1980. Report on Geology of Mong Cai – Hon Gai Area. Geological
map. scale 1/200.000. Reserved at Geological survey of Viet Nam.
4. Thanh, T. Dz. 1977. Geological History (development history of the Earth Crust).
Publishing house of university and Professional high – school. Ha Noi.
5. Thanh, T. D, N. Can and D. D. Nga. 1997. Coastal development of Do Son – Ha
Long Area during Holocene. In: Marine Geology and Geophysics. Sci and Tech. Pub.
House. Ha Noi. p. 199 - 212
6. Thanh, T. D. 1998. Geological History of Ha Long Bay. Global Pub. House and
MDHB, Ha Noi. p 1 – 94.
7. Toan, N. A. et all, 1993. Report on geology and mineral resources of Hai Phong City.
Geological map. Scale 1/50.000. Reserved at Geological survey of Viet Nam.
8. Trung, P.Q. et all, 1999. New palynological find in the Dong Ho formation.
Petrovietnam Review. Vol.3. Hanoi, p.14-20.
9. Waltham, T., 1998. Limestone karst of Ha Long Bay, Viet Nam. Engineering Geology
Report, No 806. Nottingham Trent University. UK. p.1 - 41.