♦ PhD. Nguyen Quang Anh

(Continued from Part 1)

Topographical resources

The geomorphological characteristics of the expanded Hanoi region, as presented in detail above, show that Hanoi’s topography is highly diverse in origin. Within each type, there are landform formations created during different geological periods and occurring at various elevation levels. Each geomorphological formation within the expanded Hanoi area therefore has its own distinct value.

Hilly and Mountainous Terrain

Hilly and mountainous terrain is concentrated mainly in the Ba Vi area and its surroundings. In terms of scientific value, Ba Vi is the highest mountain massif, located in the northwestern part of Hanoi. This massif was formed through the weathering of volcanic products, primarily basalt, erupted in two phases during the early Triassic period (about 240 million years ago). With elevations exceeding 1,200 m, the Ba Vi massif functions as a natural “climate regulator” for Hanoi. Regarding geological diversity, considering the geological formations exposed at the surface, the expanded Hanoi region contains a greater variety than any other locality in the country. There are as many as 17 geological formations, differing in rock composition (from consolidated to unconsolidated), origin (metamorphic, sedimentary, and igneous), and age (Proterozoic, Paleozoic, Mesozoic, and Cenozoic). The oldest is the Con Voi Mountain Formation, exposed in the Vi Thuy - Yen My (Son Tay) area, dating back to the Paleoproterozoic era (over one billion years ago), while the youngest is the Thai Binh Formation, formed only a few thousand years ago.

Aesthetic Value: The Ba Vi mountain massif extends in a north - south direction, with a fairly steep western slope and a relatively gentle eastern slope. Therefore, from the shore of Suoi Hai Lake, about 10 km to the north, all three peaks can be clearly seen. From the summit of Ba Vi Mountain, the surrounding landscape is visible in great clarity. One location of notable aesthetic value on Ba Vi Mountain lies at an elevation of about 400 m (Code 400). This is one of the extensive planation surfaces, and from this point one can look northward to observe landscapes transitioning from hills and mountains to plains and extending to the Red River. The aesthetic value of Ba Vi Mountain has long inspired poetry and music. Its scenic beauty was also one of the criteria for being engraved on the Nine Dynastic Urns (Cửu Đỉnh) of the Nguyen Dynasty.

In addition, the slopes of the Ba Vi mountain massif feature many small streams and waterfalls of high aesthetic value, such as Bac Waterfall - Sao Stream, Tien Stream - Da Waterfall, and Nga Stream, all of which have year - round flowing water. Today, some sections of these streams have been dammed to form lakes and ponds, including Ao Vua and Tien Sa Lake, among others.

Cultural Value: The legend of Son Tinh - Thuy Tinh associated with Ba Vi Mountain has become deeply embedded in the spiritual culture of the Vietnamese people. Son Tinh (Saint Tan) is said to have raised the mountain to win the battle against Thuy Tinh. To commemorate his merits, the Vietnamese built the Thuong Temple on the summit of Vua Ba Peak to worship Saint Tan (Son Tinh) - one of the “Four Immortals” (Tứ Bất Tử) in Vietnamese spiritual consciousness.

Geomorphological Map of Hanoi City [1]

The Ba Vi mountain region was also an important strategic base during both the resistance war against the French and the resistance war against the Americans. Owing to its rugged terrain, convenient access by both river and road, and its proximity to Hanoi, the Ba Vi area - specifically Da Chong - was chosen as a meeting site of the Politburo during the period of intense U.S. bombing. It later became the place where the embalmed body of President Ho Chi Minh was preserved before the liberation of the South and the reunification of the country. In recent years, the Party and the State have built a temple dedicated to President Ho Chi Minh on the summit of Nui Vua, the highest peak of Ba Vi Mountain, at an elevation of 1,296 m.

Functional Value: In terms of functional value, topography also serves as a pillar of ecosystems. Along altitudinal belts, Ba Vi Mountain acts as a core support for hill and low - mountain ecosystems, including both aquatic and terrestrial ecosystems. Thanks to the geological diversity mentioned above, ecosystems in the Ba Vi Mountain area and its surroundings also exhibit a high level of biodiversity. This is one of the key reasons why the Ba Vi area has been recognized as a National Park.

Economic Value: The most readily apparent economic value of the Ba Vi hilly and mountainous region lies in tourism development, with a wide range of forms, including scientific research, field trips for school pupils and university students in related disciplines, ecotourism, and spiritual - cultural tourism. At present, the Ba Vi mountain area and its surrounding zones have also been planned as a key ecological tourism region of Hanoi.

Limestone (Karst) Terrain:

Terrain developed on limestone is referred to by scientists worldwide as karst. Limestone terrain has distinctive surface characteristics that differ markedly from landforms developed on other rock types and is therefore easy to recognize. In the expanded Hanoi region, limestone terrain is mainly distributed in parts of the Phuc Tho - Ha Dong area and parts of the Thanh Oai - Thuong Tin - My Duc area. Limestone itself is a geological resource belonging to the construction materials group (used for lime production, building stone, and road surfacing) or as a raw material (in cement production). In terms of scientific value, limestone is a rock type that can be dissolved by flowing water, especially natural waters such as rainwater, river water, and stream water. The dissolving action of water on limestone has created a wide range of surface landforms - from karren (lapies) to tower - or cone - shaped limestone hills, sinkholes, and valleys - as well as caves. Within the My Duc limestone massif, all of these landforms are present. Typical surface features include cone-shaped karst peaks and karst valleys, notably the Yen Stream, which has developed along a fault cutting through the limestone massif in a northwest - southeast direction. Huong Tich Cave in Huong Son Commune, Hoang Xa Cave, and Cac Co Cave in Quoc Oai Commune are caves containing stalactites and stalagmites, which are formations created from limestone.

Aesthetic Value: The limestone massifs themselves form an extremely unique landscape on the Earth’s surface. Most limestone formations are majestic and rugged, while also displaying many unusual and striking shapes. This is evident in the picturesque landscape of Yen Stream - Huong Tich Mountain in Huong Son Commune, as well as in the prominent limestone hills rising sharply from the flat plains, such as Sai Son (Thay Mountain) and Hoang Xa in Quoc Oai Commune. The beauty of the limestone mountain landscape is further enhanced by the construction of artificial lakes, stretching from Quan Son Lake to Tuy Lai Lake in Phuc Son Commune. In addition to the grandeur and beauty of surface landforms, the caves within the limestone massifs also possess their own distinctive charm. Huong Tich Cave was honored in the 18th century by Lord Trinh Sam as “Nam thien de nhat dong” (the most beautiful cave in the Southern Heaven). Inside the cave, numerous stalactites and stalagmites of varying shapes and sizes create a sense of mystery and uniqueness.

Cultural Value: As a general rule, almost all limestone massifs in Vietnam, as well as around the world, contain valuable cultural imprints, including spiritual, historical, and archaeological heritage. The limestone mountain regions of Hanoi are no exception. In the Huong Tich Mountain area, there is the Lung Sam archaeological site, associated with the Hoa Binh Culture, dating to approximately 11,000 - 8,000 years ago, also known as a cave - dwelling culture. The most evident traces of this culture are the fossilized mountain snail shells observed at the entrance of Hoang Xa Cave, similar to those found at the entrance of the Ancient Human Cave in Cuc Phuong National Park, Ninh Binh Province.

(To be continued...)