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Barrier Lakes
When the volcano lava intercepts the river valley, or the landslide caused by the earthquake etc. dams the river valley or the riverbed, the upper river valley or river bed may turn into barrier lakes . The lakes formed due to the inception of volcanic rock flow are called volcanic barrier lakes .
The forming process of a type of tectonic lakes-the rift lake is:
- an already existing river system
- the original river systems are blocked up by the stem, which can be volcano lava or mud-rock flow from landslide caused by seismic activity.
- after the river valley and riverbed are blocked up, the flowing water assemble and overflow around.
- when the water is stored to a certain extent, the barrier lake takes into shape.
 In China, Wudalianchi in the Northeast is once called Naodelin Pool, situated in the outskirts of Wudalianchi City. It is located in the upper reaches of the White River, a tributary of Nanuo'er River, only 30.0 km to the north of Small Xin'anling Mountains. The basalt lava that two volcanoes, Laohei Mountain and Huoshao Mountain sprayed and spoiled over blocked up the White River and formed 5 small lakes linked to each other like one bunch of pearls.
The volcanic activities Wudalianchi Volcanic Group started from late Jurassic period to early Cretaceous period. According to historical record, the most recent volcano eruption started from 1719 (the 58th year of Kangxi Reign in Qing Dynasty). In the 'Unofficial History of Heilungkiang' it reads, "to the southeast of Mo'ergen, one day, the fire suddenly came out of the ground. The stone soared, and its sound went beyond all around. The fire went out after about several days, and its ground then presented ponds." The volcano eruption blocked up the White River-original tributary of Nahan River, and forced its riverbed moving eastward. The river was obstructed and formed 5 prayer beads like lakes run through by the Shilong River.
 The lake water in Wudalianchi is limpid and resembles a mirror, which reflects the cloud shadows and shining lights.
In Jingbo Lake in Heilongjiang Province, there is a natural imprisoned dyke, 40m wide and 12m high, which was formed by the basalt flow near the Diaoshui Floor during the Quaternary Period, which intercepted the Mudanjiang exit, raised the water level and formed the typical lava-dam lake with an area of 90.3 km2. The lake is surrounded by hills, covered by dense forest, and presents a pretty scene. There are not only the crater forest, grotto and ruins of Bohai Sea in the Tang Dynasty, but also the "Eight Famous Scene," including Big Hu Mountain, Little Hu Mountain, Pearl Door, Diaoshuilou Waterfall and Jingbo Mountain Villa. Thus it becomes a famous lake among the tourists in China.
The imprisoned or barrier lakes formed due to landslides are mostly seen in the valleys of Southeast Tibet and are generally with young age. For instance, in the northwest of Simla in 1819, there formed a lake, 24-80 km long and 122 meters deep, because of the landslide. In the Bome county of Southeast Tibet in 1990, the enormous mud-rock flow caused by the breakout of earthquake intercepted the Zhalongqiu River and formed the Yi'ong Co. Guxiang Co in Bome County was formed by the glacier mud-rock flow in 1953. (actually also belonging to glacier lake). In 1959, Ra'og Co in Baxoi County was formed due to the jam of river valley by the landslide.
The seismic activity in Taiwan Province is frequent. In December of 1941, a strong earthquake happened in the Northeast of Jiayi, and caused landslide, which blocked up the east section of the Zhuoshuixi River. A dyke of 100m high formed in the river with an elevation of 580m, and ten months later, the water in the upper reaches accumulated and formed a barrier lake with an area of 6.6km2 and a depth of 160.0m.
The great landslide in Yi'ong Zangbo of Tibet caused the forming of the latest barrier lake in April, 2000. There flows the Yi'ong Zangbo on the Yi'ong Basin before the landslide, but the river was distributed in a net shape, with a total area of 26km2. After being jammed, the river becomes a large lake with an area of 33km2 .
It must be stressed that the stems for the barrier lakes is not steady , and they may be washed out, eroded, dissolved, or even collapse. Once the stem is destroyed, the lake water will overflow and come down in torrents, forming the big flood, which is extremely dangerous.
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