Da Dia Reef is located in Tuy An Dong Commune, Dak Lak Province. The site is approximately 50 meters wide and stretches for more than 200 meters, forming a rare natural landscape. According to geological studies, the rocks at Da Dia Reef are basalt, formed by volcanic eruptions millions of years ago.
Da Dia Reef is located at approximately 13°35’39” N latitude and 109°29’37” E longitude. Its name derives from the distinctive shape of the basalt formations. As volcanic lava cooled, contracted, and fractured, it formed relatively uniform polygonal columns. Subsequent geological movements and marine erosion exposed these formations, creating layers of rocks resembling stacks of plates.
Da Dia Reef is situated within a diverse coastal landscape where hills and mountains extend toward the East Sea. Some areas slope gently toward the sea, such as Bai Bang, while others remain considerably elevated, including Da Dia Reef and Mom Cape.
Geology and Formation
Da Dia Reef is the result of geological processes that have taken place over millions of years, associated with volcanic activity and the evolution of the coastal landscape of Phu Yen.
The coastline of Phu Yen is a typical part of the South Central Coast, where prolonged interaction between the mainland and the East Sea has shaped a variety of coastal landforms. Successive periods of marine transgression and regression, together with tectonic uplift, subsidence, faulting, and erosion, have contributed to the formation of distinctive coastal features.
The area north of Da Dia Reef is mainly composed of granite belonging to the Deo Ca complex, with a geological age of approximately 70–127 million years. Meanwhile, strong volcanic activity occurred in central Phu Yen, particularly around the Van Hoa Plateau.
After erupting from volcanic vents, basaltic lava cooled and contracted, producing a system of polygonal fractures. These fractures divided the solidified lava into columns with pentagonal, hexagonal, and other polygonal cross-sections. Subsequent tectonic uplift, changes in sea level, and continuous erosion by waves and wind gradually exposed the basalt columns along the coast, creating the distinctive landscape of Da Dia Reef today.
Geological studies indicate that the basalt of Da Dia Reef is distributed over a relatively extensive area, extending southwestward across Mai Nha Mountain to the Ha Yen River estuary. South of the Ha Yen River estuary, the basalt is divided into isolated hills, while to the west lies the basaltic plateau of Van Hoa.
Studies of the absolute ages of basalt formations in the Van Hoa and Song Cau areas indicate several different age ranges, including approximately 0.7–1.55 million years, around 5 million years, and approximately 7.01–10.5 million years. For the basalt at Da Dia Reef, the most plausible age is estimated to range from approximately 5 million to 0.7 million years ago, corresponding to the Pliocene to Early Pleistocene.
The combination of volcanic eruptions, cooling and contraction of lava, tectonic movements, and prolonged marine erosion has created an extraordinary basalt formation that has become one of the most distinctive geological landscapes along the coast of Phu Yen.
Landscape and Main Areas of Da Dia Reef
The protected area of the Da Dia Reef scenic landscape covers approximately 200 hectares, including Area I of 11.3 hectares and Area II of 188.7 hectares. The landscape consists of several distinctive geomorphological areas, notably the basalt column zone, the northern coastline, Bai Bang, Mom Cape, and the western marine terrace.
Basalt Column Zone
This is the central and most characteristic area of the scenic landscape, covering approximately 2,700 square meters. The basalt columns emerge from the shoreline in two small rocky promontories extending toward the sea.
The northern promontory extends for more than 40 meters from the coastal cliff and reaches a maximum width of approximately 30 meters. Its lower section consists of vertical or slightly inclined basalt columns, approximately 2 meters high, gradually becoming lower before disappearing beneath the sea. The middle section contains columns that curve and gradually transition into a horizontal position. Above them is a layer of horizontally arranged columns approximately 5 meters high, with regular cross-sections that resemble the end of a gigantic bundle of chopsticks.
On the southern side of this promontory, the basalt columns are strongly affected by waves. Continuous wave action widens the existing fractures and gradually separates individual rock blocks from the main formation.
The second promontory lies to the south, where the basalt columns are almost vertical and form three distinct geomorphological levels. The lowest level extends approximately 9 meters toward the sea and rises about 0.5–1 meter above sea level. The middle level is approximately 3.5 meters higher than the lower level and set about 3 meters farther inland. The upper level is approximately 2 meters higher than the middle level, lies close to the shore, and supports vegetation.
The curved arrangement of the basalt columns and the polygonal fracture system are among the most distinctive geological features of Da Dia Reef. Approximately 11,500 basalt columns are exposed here, mainly with pentagonal and hexagonal cross-sections. The average diameter of the columns is approximately 43 centimeters, while the average thickness of the individual “plates,” measured between transverse fractures, is approximately 25–30 centimeters.
Basalt columns also continue beneath the sea in front of Da Dia Reef, extending approximately 20 meters offshore. The formations gradually descend into deeper water farther from the shoreline.
At the southwestern edge of Da Dia Reef stands Lang Da Dia, a small sacred site dedicated to the Sea God, or Ca Ong, according to the traditional beliefs of local fishing communities. The structure was built around the mid-19th century during the reign of Emperor Tu Duc and was restored in the 1980s.
Northern Coastal Area
From the northern side of the central basalt formation, the scenic landscape extends toward Ganh Den at the entrance to Xuan Dai Bay. The coastline here is primarily composed of granite cut by fracture systems running in different directions and varying in size.
The granite formations display various colors, including white, pink, and brown. Weathering and wave action have gradually broken down and reshaped the rocks, creating fields of boulders and pebbles with diverse and striking forms.
In some locations, subsidence and strong marine erosion have created nearly vertical cliffs, some more than 20 meters high. The rocky formations extend toward the sea, with some sections reaching approximately 300 meters from the shoreline.
Bai Bang Area
Bai Bang lies south of Da Dia Reef and features a crescent-shaped beach formed from basalt and granite formations that have been extensively eroded by the sea.
The northern part of the land area is relatively flat, while the southern section gradually rises westward, reaching approximately 50 meters near Mom Cape. The seabed in front of Bai Bang is relatively flat, with the widest distance from the shoreline to the boundary of the protected area measuring approximately 750 meters.
The sea area south of Bai Bang borders Mom Cape, where various types of seaweed grow.
Mom Cape
Mom Cape forms the southern continuation of Bai Bang. It is a mountain extending westward, while subsidence near the coast has created a steep sea cliff approximately 20 meters high.
At the foot of the cliff is a rocky shore shaped by wave erosion. It extends approximately 50 meters eastward and gradually descends beneath the sea. The rocks at Mom Cape are also columnar basalt, although their forms are less distinctive and visually pronounced than those at the central Da Dia Reef area.
Western Marine Terrace
The marine terrace lies immediately west of Da Dia Reef and has an elevation of approximately 4–10 meters. It was formed through processes of marine erosion and deposition during the evolution of the coastal landscape.
Native vegetation grows across the terrace, including duoi, son trang, giao, and thom tau, together with various herbaceous plants that develop strongly during the rainy season. Some areas of the terrace near Da Dia Reef have been cleared for seasonal agricultural production.
Flora and Fauna
The diverse terrain and coastal climate support a relatively varied ecosystem around Da Dia Reef.
Terrestrial vegetation mainly consists of species adapted to dry conditions and exposure to sea salt, including tropical almond, cactus, giao, thom tau, and various herbaceous plants. Vegetation develops more strongly during the rainy season, particularly on the marine terraces and coastal land.
The terrestrial fauna includes several species of seabirds and migratory birds, including terns and swiftlets, as well as other species adapted to coastal environments.
The waters surrounding Da Dia Reef support a diverse marine ecosystem, including fish and crustaceans characteristic of the central Vietnamese coast. Several species have significant economic value, including groupers, snappers, and lobsters. These marine resources are closely associated with fishing activities and the livelihoods of coastal communities in Phu Yen.
Heritage Value of Da Dia Reef
The outstanding value of Da Dia Reef lies first in its distinctive geological structure, which was formed through ancient volcanic activity. Thousands of basalt columns with polygonal cross-sections, particularly pentagonal and hexagonal columns, together with their curved, stacked forms and continuation beneath the sea, create a landscape of considerable scientific and aesthetic value.
Da Dia Reef is also part of a diverse coastal geomorphological complex comprising basalt, granite, marine terraces, rocky beaches, sea cliffs, Bai Bang, and Mom Cape. The combination of these landforms creates a distinctive landscape characteristic of Vietnam’s South Central Coast.
In addition to its geological and geomorphological significance, Da Dia Reef is closely associated with the cultural life of coastal communities. This is reflected in Lang Da Dia and the traditional worship of the Sea God, or Ca Ong, among local fishing communities.
With its outstanding geological, geomorphological, scenic, and cultural values, the Da Dia Reef Scenic Landscape was recognized by the Prime Minister of Vietnam as a Special National Relic under Decision No. 2280/QD-TTg dated December 31, 2020.
Today, Da Dia Reef is one of the important heritage landscapes of Dak Lak Province and a site of significance for geological research, environmental education, landscape conservation, and tourism development. The basalt columns formed millions of years ago continue to be shaped by waves and other natural processes, preserving a remarkable geological landscape for future generations.
