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Halong Bay Travel Guides
Value
of Geology
             
The most remarkable geological events of Hạ Long Bay’s
history in the last 1,000 years include the advance of the sea, the
raising of the bay area and the strong erosion that has formed coral and
pure blue and heavily salted water. This process of erosion by seawater
has deeply engraved the stone, contributing to its fantastic beauty.
Present-day Hạ Long Bay is the result of this long process of geological
evolution that has been influenced by so many factors. Some of the most
remarkable are: the formation of the limestone layer more than 1,000 m
thick during the Carboniferous and Permian periods (240 to 340 million
years ago); and the development of the Hạ Long depression during the
Neogene period (10 to 26 million years ago). The erosion process forming
the limestone plain was most active in the Quaternary Pleistocene epoch
(11,000 to 2 million years ago). It is because of all these factors that
tourists now visiting Hạ Long Bay are not only treated to one of the
true wonders of the world, but also to a precious geological museum that
has been naturally preserved in the open air for the last 300 million
years.
At the beginning of the Cambrian era (500 to 570 million years ago), the
area, which now forms Hạ Long Bay, was basically mainland, submitted to
a process of rain erosion. At the end of the period, it was flooded,
commencing the existence of Hạ Long Bay. During the Odovic and Silurian
periods (400 to 500 million years ago), the area of north-east Vietnam
was basically a deep sea, submitted to the constant activity of tectonic
plates. At the end of the Silurian period, it underwent a phase of
inverse-motion that created mountains deep under the water. From the end
of this period and throughout the whole Devonian period (340 to 420
million years ago), the area was subjected to powerful forces of erosion
from the hot and dry climate. At this point, Hạ Long was part of a wide
mainland that comprised most of today’s East Sea and Chinese continental
shelf. Due to tectonic activity, the Hạ Long area and the entire
north-east region were raised from the depths at the end of the Devonian
period. In the later Carboniferous and Permian periods (240 to 340
million years ago), a shallow and warm sea reformed, which existed for
approximately 100 million years. It created two kinds of limestone: the
Cát Bà layer of the early Carboniferous period (450 m thick); and the
Quang Hanh layer of the middle Carboniferous and the early Permian
period (750 m thick). These two layers constitute the majority of the
islands of the Bay.
Passing into the early periods of the Contemporary era (67 million years
ago), Hạ Long Bay existed in the environment of a high mountainous
mainland due to the influence of strong mountain-forming phases. The
middle of the Paleocene period saw these motions remain continuous and
stable, while strong processes of erosion began, and after millions of
years, a form of semi-highland topography took shape. The continuation
of this erosion has progressively cut the highlands into blocks with
altitudes similar to today's mountains.
Into to the Quaternary era, the process of erosion began dissolving the
limestone-rich region of Hạ Long. The islands of today’s Hạ Long Bay are
basically remnants of these mountains flooded during the early Holocene
period. Rainwater flowed into crevices in the limestone that had formed
from tectonic activity. This steady erosion constantly widened the
cracks, eventually creating today’s formations. The middle and late
Pleistocene epoch (11,000 to 70,000 years ago) marks the period when the
famous caves and grottoes of the area formed.
The Holocene period (from 7,000 to 11,000 years ago) is notable for the
advance of the sea. This movement reached its peak 4,000 to 7,000 years
ago and forming today’s Hạ Long Bay. After that, 3,000 to 4,000 years
ago, with the sea in a steady process of recession, Hạ Long culture
began to develop. At the beginning of the late Holocene epoch, the level
of the water once again increased, forming a marshy floor of canals and
streams, and creating the water marks that can be seen on the stone
cliffs of today.
Overview • Halong bay Maps • Halong Beaches • Halong Caves • Halong Islands • Transport • Other Boats • Entertainment • Festivals in Halong • Natural Beauty • Value of Geology • Cultural-Historical Value • Biological Diversity • Halong Pictures
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