A barrier of basalt
Jingpo Lake exists because of a massive geological event. Around 10,000 years ago, effusive eruptions from the Jingpo Volcanic Field sent floods of alkali olivine basalt across the landscape. This molten rock flowed into the path of the Mudanjiang River, creating a natural barrier and blocking its course. Over time, water backed up behind this impromptu dam, submerging the former river valley and forming the S-shaped Jingpo Lake. Today, the lake covers a surface area of 95 square kilometers and holds an estimated 1.63 billion cubic meters of water.
The volcanic field that created this landscape contains at least twelve distinct craters, which are now covered by a dense growth of trees and known locally as the "Underground Forest". The eruptions also formed an extensive network of subsurface lava tubes. Some of these tunnels are among the largest and most intact in China, with one measuring over 10,000 meters in length. The entire region is recognized for its geological value as a UNESCO Global Geopark.
An un-engineered floodgate
The dam holding back Jingpo Lake is not a structure made of concrete and steel, and is a thick wall of cooled basalt. Its integrity depends entirely on the properties of the volcanic rock. The lake's primary outlet is the Diaoshuilou Waterfall, a natural spillway where the Mudanjiang River cascades 20 meters over the face of the lava dam. The waterfall is approximately 40 meters wide, though its flow rate varies seasonally.
The volcanic field sits on the western flank of the Tan-Lu Fault Zone, the longest tectonic fault in Asia. The presence of this major fault system means the region is seismically active. A significant seismic event could theoretically compromise the dam's structure. The stability of this natural barrier is a constant factor for the city of Mudanjiang and other communities located downstream along the river. While the dam has stood for millennia, the immense pressure from 1.63 billion cubic meters of water against a natural rock formation in a seismically active area presents a unique geological condition.