The earthquake-dammed lake, the beautiful scenery left by the disaster in Sichuan

Among the numerous natural lakes in Sichuan, there is a kind of earthquake-dammed lake that can be said to be an alternative among lakes. Earthquake-dammed lakes are lakes formed when the mountains on both sides of the river collapse due to an earthquake, blocking the river.

Sichuan is an earthquake-prone region. Due to its special geological and geomorphological environment, especially its location in an area with many canyons, strong earthquakes often form large-scale barrier lakes.

The 7.5-magnitude Diexi earthquake in 1933 alone formed more than 10 earthquake-dammed lakes, eight of which remain today, forming a rare group of earthquake-dammed lakes. The 2008 Wenchuan earthquake formed as many as 132 earthquake-dammed lakes, of which the Tangjiashan earthquake remains today, making it the youngest earthquake-dammed lake to date.

In history, most of the earthquake-dammed lakes collapsed within a few days after they were formed, and only a few survived to be seen by future generations. When the disaster was over, these earthquake-dammed lakes that once caused great disasters and threats to mankind gradually stabilized and the threats were lifted. They lay quietly in the deep valleys, not only recording the disasters, but also becoming a beautiful landscape that people can read endlessly.

▲Songpinggou earthquake barrier lake group. Photo by andylee101 (TuChong Creative)

01 Diexi-Songpinggou

Diexi, also known as Xiling, was the place where Emperor Wu of the Han Dynasty established Canling County. It has always been an important border town in all dynasties. Together with Songzhou and Maozhou, it was an outpost for the Tang Dynasty to fight against Tubo. It is also a key point on the Henan Road connecting the Northern Silk Road and the Southern Silk Road, and an important town on the Songmao Ancient Road.

This ancient city, along with its remote and mysterious history, disappeared in an instant in the 7.5 magnitude earthquake in 1933. The Diexi earthquake formed the most complete and typical earthquake relics in China, which are also extremely rare in the world. Along the Minjiang River and its many tributaries, there were earthquake-dammed lakes, extremely spectacular collapse-landslide groups, ground fissures and earthquake fault zones, Diexi Ancient City and Qiang Village ruins, and other earthquake relics.

▲Diexi-Songpinggou earthquake-dammed lake group.

The earthquake destroyed Diexi City and 21 nearby villages, and the ancient city of Diexi moved 40-60 meters south and sank 280-300 meters. 6,865 people lost their lives instantly. More than ten earthquake-dammed lakes were formed in the X-degree epicenter area, and 8 of them are still preserved today.

They are Dahai Lake and Xiaohai Lake (Diexi Lake) on the Minjiang River, Shangbai Lazhai Lake and Xiashui Mogou Lake in its tributary Songpinggou, Gongpeng Lake and Yuerzhai Lake. During the earthquake, three weirs were formed in the Yinping Cliff, Daqiao and Diexi (Xiaoqiao) canyon sections of the Minjiang River. Later, the three weirs were connected to form a flat lake in the Minjiang River canyon. The lake is about 12 kilometers long and about 2 kilometers wide at its widest point.

At about 7 pm on October 9, 45 days after the earthquake, the Diexi Weir suddenly collapsed, and the accumulated water poured out into the lake. The waves were turbulent, roaring and roaring, and the farmhouses, fields, grains, and property in the villages and towns along the river in Maoxian, Wenchuan, and Guanxian were swept away, causing heavy casualties among people and livestock. Even the Fish Mouth and Feisha Weir of Dujiangyan were damaged. Today, this is still one of the most well-preserved earthquake-damaged sites in the world, and it can be called one of the best on the Nine Ring Road.

▲Songpinggou earthquake-dammed lake group. Illustration by Yang Jinshan

Diexi Lake is actually a section of the mainstream of the Minjiang River. It is a barrier lake formed by an earthquake. The lake is only about 1 km wide, but it is 10 km long. The deepest part of the lake is 98 meters, and the average depth is 82 meters. The lake is formed by two connected parts, shaped like a bean pod. Surrounded by green mountains, the lakeshore is covered with lush grass, the lake water is rippling, and the scenery is beautiful and charming. On June 15, 1986, the lake burst again, and 1,200 tourists were trapped. If the weather is clear, you can clearly see the city walls, arches and streets that collapsed into the water that year through the clear lake water.

In the ruins area of ​​Diexi Ancient Town, you can still see the remnants of the East City Gate, the stone tablets and pillars of the City God Temple; the gunpowder mill of the gunpowder bureau, the only preserved section of the city wall and the huge stone engraved with "Canling Important Town", the Fan Lihua general platform that cracked in the earthquake, and the remains of Suosuo Village formed by stepped collapse, making this one of the most complete earthquake sites in the world.

Songpinggou originates from Luzilanggu in Riduowo Mountain, with a total length of 39 kilometers. It is 12 kilometers away from the Diexi earthquake site. Songpinggou is characterized by the pearl-like earthquake-dammed lakes, mainly including Baishihai, Mohai, Shangxia Bailahai, Changhai, and Yuerzhai.

▲Diexi Lake. Photo by Yang Jian

02Lepoma Lake

Mahu Lake, also known as Longma Lake, is called "Halangshuhuo" in Yi language. It is the third largest natural deepwater lake in Sichuan, on par with Qionghai Lake and Lugu Lake. It is 47 kilometers away from Leibo County. It is said that the ancients tied a mare to the lake shore, and a dragon came out of the lake and mated with it to give birth to a strange horse, hence the name. It is 1,100 meters above sea level, 5.63 kilometers long, 1.3 kilometers wide, 2.3 kilometers wide at its widest point, with a water area of ​​7.24 square kilometers, a water storage area of ​​481 million cubic meters, an average water depth of 66 meters, and a maximum depth of 134 meters. It is the fourth largest known deepwater lake in my country, and also the largest earthquake-dammed lake in China and a rare one in the world.

Mahu Lake is a high mountain lake and a tributary of the Jinsha River. Three small streams flow into the lake from the south. The basin area is 106 square kilometers. The entire basin is fan-shaped with a length of 12 kilometers from north to south and a width of 8.5 kilometers from east to west. The south, north and east sides are low and the west side is high. The main streams are Ezigou, Dongbugou and Xibugou. Among them, Dongbugou has the largest water volume, followed by Ezigou and Xibugou has the smallest water volume. Mahu Lake is a complete and independent hydrological unit. The lake water is mainly replenished by atmospheric precipitation. The lake water is discharged from south to north through underground runoff. The rock composition at the bottom of the lake has good water-repellent properties, which is why the water of Mahu Lake can gather here.

▲The small island in Ma Lake. Photographed by Xiao Yitu (TuChong Creative)

Mahu Lake, located in the canyon, is surrounded by mountains on three sides, and the Jinsha River roars past from its east side, with beautiful scenery. Mahu Lake is like a crescent moon on the plane, with deep harbors in the lake area, winding and changeable lakeshores, smooth and delicate rock layers at the bottom of the lake, and clear and transparent lake water. There are a total of 10 large harbors and 3 small islands. There are dozens of scenic spots around it, including Longhu Cave, Dahaibao (Golden Turtle Playing in the Water), Hippocampus Stone, Sow Lying Cliff, Goose Flying Crossing, Five Horses Returning to the Trough, Dasuoyue, Tianmen Xiongchen, Blue Snake Chasing Turtle, Jinhai Mountain Reclining Buddha, Monkey Rock, Zhuge Liangdian General Platform, etc. There is also an outlying island - Golden Turtle Island and a peninsula - Shuanghaibao, on which there is the only Yi temple in the country, Menghuo Temple.

Mahu Lake is beautiful in all seasons. In spring, the lake is full of rippling water, and peach, pear and azalea trees are blooming on both sides of the lake. In midsummer, the lake is full of clear water and blue sky, and the mountains are covered with emerald green. In autumn, the lakeside is full of fragrant rice flowers, and the surrounding mountains are full of colors. In winter, the lake is surrounded by a vast sea of ​​snow and the weather is freezing, but Mahu Lake is still full of green water, like a sapphire inlaid on white jade.

▲Mahu Lake. Photo by Yang Jian

There have been many different explanations for the formation of Mahu Lake. Some people believe that it is a glacial barrier lake formed by the melting of the Quaternary glaciers 2 million years ago, and the accumulation of moraine rocks into embankments and water accumulation; some people believe that it is a karst lake formed by karst collapse; and some people judge that it is a tectonic fault lake formed by tectonic faults based on the structural development of the area where Mahu Lake is located. However, recently, many geological experts have inferred that Mahu Lake is a tectonic earthquake barrier lake formed by the collapse of a mountain formed by an earthquake and blocking the river channel based on the geological background, embankments, and the shape and characteristics of the deposits around Mahu Lake, as well as the distribution shape and characteristics of Mahu Lake.

Mahu is located on the south side of the Liangshan block active fault tectonic zone, and the new tectonic activity is relatively strong. The active faults are the Laoyingpan Fault and the Ziba Fault. These two faults have caused many earthquakes in history, such as a magnitude 7.0 earthquake on March 17, 1216. According to historical records, this earthquake caused "80 miles of landslides in the Mahu Yijie area, and the river was blocked." So was Mahu formed by this earthquake? The answer is no. Because as early as 2,000 years ago, Mahu and Huanglang were both established as counties and prefectures many times. They are the ancient towns with the longest history, the most developed culture, and the most important location in Leibo County. There are long-standing written records in historical records that "Mahu was Linchiqian in the Western Han Dynasty, and the lake water flowed into the Jinsha River." This shows that in the Western Han Dynasty, Mahu, which was blocked by the Huanglang River, already existed, but the Mahu earthquake in 1216 occurred 1,300 years later.

The formation time of Mahu Lake seems difficult to determine. Fortunately, the Mahu Lake embankment and the earthquake deposits widely distributed around it provide us with a basis for solving the mystery. Geologists have finally determined that the Mahu landslide body is a group of prehistoric ancient landslide bodies through the study of the composition and shape of the landslide deposits. It was formed by several large-scale landslides between the early Middle Pleistocene and the early Late Pleistocene. There have been five landslides from east to west. The huge landslide deposits produced by these five landslides blocked the ancient Huanglang River, thus forming Mahu Lake. Among them, the latest landslide dam is 110,000 years ago.

▲The small island in Ma Lake. Photo by Yang Jian

03Tangjiashan Dammed Lake

Tangjiashan is located in Beichuan Qiang Autonomous County, and its barrier dam is located 4 kilometers upstream of Qushan Town, the old county seat of Beichuan. The Wenchuan earthquake on May 12, 2008 caused a large number of landslides in Tangjiashan. Two adjacent huge landslides mixed with boulders and soil rushed to the Jianjiang River, forming a huge barrier lake. The barrier dam is 803 meters long, 611 meters wide, 82.65 to 124.4 meters high, with a volume of about 20.37 million cubic meters, and a water level difference of about 60 meters between upstream and downstream.

The "512" earthquake formed 132 barrier lakes in Sichuan, among which the Tangjiashan barrier lake was the one with the highest danger level and the greatest potential threat. Should this natural "hanging lake" formed in an instant be dealt with? How to deal with it? It became the focus of great attention around the world at that time. But people's painful memories of earthquake barrier lakes quickly helped us make up our minds. According to records, the Kangding earthquake in Sichuan in 1786 and the Diexi earthquake in Sichuan in 1933 both formed barrier lakes. The collapse of the barrier lake caused the number of deaths downstream to be several times that of the earthquake. According to scientific research, 21% of the barrier dams collapsed within 1 day after formation, 48% collapsed within 10 days, 78% collapsed within 6 months, and 88% collapsed within 1 year. For the Tangjiashan barrier lake, if there is no human intervention, once it collapses, its destructive power will exceed the historical tragedy and create a new disaster record.

▲Tangjiashan barrier lake disaster relief site (@Source: Internet)

Thus, an unprecedented century-long rescue operation was launched. Starting from May 26, dozens of bulldozers, excavators and other heavy machinery were transported to the dam body by a Mi-26 helicopter and five Mi-17 helicopters rented from Russia. Thousands of armed police hydropower officers and soldiers also arrived. After nearly a month of arduous struggle, a flood discharge channel about 500 meters long, 50 meters wide and 12 meters deep was completed. On June 7, the discharge channel began to drain water. On June 10, the flow of the discharge channel increased rapidly. The huge turbidity current, carrying mud and sand, rushed out with great momentum and unstoppable force. The crisis of the lake hanging over the heads of more than 2 million people in the downstream disaster area was resolved. The Tangjiashan barrier lake created a miracle in the history of world rescue and disaster relief.

When all the crises were over, the Tangjiashan barrier lake lay quietly among the mountains, peaceful and tranquil. In 2011, due to the drop in water level, the Xuanping Town, which had been submerged under water, reappeared for the first time in three years, which made people sigh.

For a period of time, there were different controversies about whether to remove or retain this large barrier lake. After much discussion, it was finally decided to retain the barrier lake and build it into a 5A scenic spot together with the earthquake site of the old Beichuan County. Today, the Tangjiashan Barrier Lake Management Bureau established in Mianyang City, Sichuan Province has completed the treatment of cracks on the left bank of the barrier lake and landslides on the right bank, the barrier lake discharge channel, the emergency treatment of the large landslide body of Tangjiashan, and the flood control embankment of Yuli Township, as well as supporting projects such as pedestrian cable bridges and emergency rescue roads. The former "water demon" is becoming a beautiful home and a beautiful scenic spot that retains the memory of the "5.12" earthquake disaster, inherits the long humanistic history and splendid national culture of the Qiang people, and records the great spirit of earthquake relief and boundless love culture.

▲The Tangjiashan barrier lake today, photo by Qiu Shi (TuChong Creative)

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References:

Li Zhongdong, Tan Yibo, et al., Sichuan in the World - The Best Guide to Sichuan Fun, China Tourism Press, 2014;