An outdoor geological museum of Trang An complex

Harmonic mixture of nature, mountain, rivers, animals, plants has created unique picture with its own aesthetic and landscape value that cannot share with nowhere worldwide.

Outstanding value of Trang An is karsts geomorphology. Karsts limestone mountain range of Trang An belongs to the hindmost part of that of ancient Tethys ocean which runs from Southeast China to Vietnam. These mountain ranges have formed a unique limestone highland in Northwest of Vietnam.

The mountain range turned into separate mountain blocks when it is in Trang An complex, decreasing in height from the northwest to the southeast, as it slopes to the sea.This is exclusive character of Trang An in particular as well as of mountain range of Northeastern region in general.

The Trang An Scenic Landscape Complex is most characterized by its superlative large-scale karst towers and bell-shaped karst outcrops eroded by sea water.Turbulent Earth movement plus with climate changes, sea transgression have formed fault block mountains.

In particular, the area contains important examples of the so-called "fengling" and "fengcong" karst formations, with the typical "fengcong" topography shown in the area's large and super- large enclosed valleys and sinkholes. The Trang An area serves as the global type site reference for these unique geological formations.

The outstanding geological value of TRang An has affirmed by both foreign and domestic scientists. The geologic - geomorphologic diversity present in the Trang An Scenic Landscape Complex resulted from continuous geologic activities over the hundreds of millions years. Geomorphologic collapse and high fragmentation of huge sedimentary limestone karst blocks took place. These complex geologic movements created the majestic mountains, sedimental basins and sinkholes which together have resulted in the diversity of the topographic, geomorphologic, cave and water systems of the Trang An Scenic Landscape Complex.

Tectonic structure of "Cracking dry pancake" of Trang An make it the only representative for karstification process of periodical development from the outer toward center such as distribution of karsts landscape as follows: separated karsts hills, sinkholes, connected peaks of sinkhole basins, connected peaks of valleys.

In particular, though it looks like Ha long bay in term of landscape, Trang An complex is total dry, not submerged under water sea. The geology of the Trang An Scenic Landscape Complex dates from the glacial and interglacial episodes of the Quaternary when rates of erosion were accelerated due to the great fluctuations in climatic conditions. During this time of repeated sea-level rise and subsequent inland flooding, the region was subjected to periodic inundation. The wave cuts found at the base of most of the limestone karsts within the property are the result of environmental and climate fluctuations during, and especially, at the end of the Quaternary. Within the Trang An Scenic Landscape Complex there are numerous caves from this period which are situated on marine terraces of different heights corresponding to sea levels changes correlated to the chronology of the interglacial periods, giving evidence that this was a time of generalized global warming.

Scientists found that sea wave cut dates from Holocene era between 23,000 BCE until recent times, and in particular through the period of the post-Pleistocene rise of sea levels world wide as a global warming and the consequent melting of ice, flooding many coastal and low-lying areas known as the Flandrian Transgression.

Naturally, basin formation depends totally on development of delta: silt deposited along the shoreline, gradually heightening the shore, and enlarging shore, in addition with process of making dyke, silt cannot access the other side of the dyke, so it easily become a basin, in tandem with pushing the shoreline further inland. So did with Hoa lu ancient sea.

Receding sea water left trace in mountain cliffs such as wave cuts, deposits of the shells of fresh water and marine mollusks, dry caves, flooded caves…Together with working tools, made of stones, bones and shells, earthenware and jewel articles, wooden boat-coffins, Han-era tombs, construction materials, including a diversity of bricks and double diamond shaped decorative tiles dating from the 10 th century are the strong evidence for human occupation in ancient time.

The labyrinth of mountains, caves, and waterways of the Trang An Complex provided effective protection for local defenders against invading Chinese imperial troops. Nor is it surprising that the first capital of the Vietnamese feudal and independent state, Hoa Lu, was established here more than 1,000 years ago, relying on the very rugged karst landscape as a favorable, safe and easily defended citadel.

(Translated by: Nguyễn Thủy)