Hot springs and fumaroles signal active magma. The last eruption was possibly in 1609 CE, making it one of China's few potentially active volcanic systems.
STW932, CC BY-SA 4.0, via Wikimedia Commons
A Field of Fire
The Tengchong Volcanic Field, located on the southeastern edge of the Tibetan Plateau, is the direct result of the immense geological forces of the Indo-Asian continental collision. This area contains at least 68 volcanoes, most of which are pyroclastic cones, with around 25 still having recognizable craters. The field is spread over approximately 800 square kilometers.
The most prominent and youngest volcanic cones are Dayingshan, Ma'anshan, and Heikongshan. Dayingshan is the highest, reaching an elevation of 2,865 meters. The geology of the field is complex, a product of multiple eruption phases from the late Miocene to the Holocene. The rock composition is predominantly a high-potassium calc-alkaline suite, including basalt, dacite, and various forms of andesite. This specific chemistry shows a magma source formed by the interaction of subducted continental crust and the Earth's mantle. The entire volcanic region sits on a thinned section of crust, measuring about 34 to 38 kilometers thick, which is significantly less than the surrounding areas.
Subterranean Heat and Seismic Clues
The most striking evidence of ongoing geological activity is the area's intense geothermal system. The Tengchong field contains over 80 hot springs and vapor vents. The largest and most active of these is the Rehai Geothermal Field, also known as the "Hot Sea," which covers nine square kilometers. Water temperatures here can be extreme; the "Big Boiling Pot," a spring with a diameter of about three meters, reaches temperatures of 97°C.
This surface heat is a direct result of a magma chamber deep below. Seismic surveys have identified low-velocity zones in the crust that indicate the presence of molten rock. One study suggests the presence of a large magma reservoir at a depth of 20-35 kilometers with an estimated melt volume of 140 to 315 cubic kilometers. Another study points to a magma source region between 10 and 20 kilometers deep. This magma system is considered unstable and is fed by a deeper source in the upper mantle. Historical records, including the travel notes of Ming Dynasty geographer Xu Xiake, describe a possible explosive eruption at Dayingshan in 1609 CE. While the last confirmed large eruption was much earlier, around 5750 BCE, the geothermal activity and seismic data confirm that Tengchong's volcanic system remains active.
💡Fun Facts
The region is the only Quaternary volcanic area within the Himalayan Geothermal Belt.
Some hot springs have unusual local names, such as the "Pregnant Well," once believed to heal certain illnesses.
The local saying, "On the Tengchong land, nine out of 10 mountains have no head," refers to the flat-topped volcanic cones.
Visitors can buy eggs and peanuts that have been cooked using the natural steam from the "Big Boiling Pot" hot spring.
The Tengchong Volcanic Geothermal National Geological Park is typically open from 8:00 to 18:00.
Admission
Park entry is approximately CNY 35-50. Combo tickets including the Rehai (Hot Sea) area are also available. Prices are subject to change.
Accessibility
The park includes paved paths and stairs for climbing some of the volcanic cones, such as the 1,442-step staircase on Dayingshan. The terrain can be uneven.
