Columnar joint

On the Bank of the Longchuan River in Tengchong County, Yunnan Province, there stands a large area of columnar crystal formed by the condensation of unexposed magma from the eruption. Geologically, it is called "columnar joint", while the local people vividly call it "Shenzhu".

"Shenzhu" is the largest, the most complete and the shortest columnar joint discovered so far in China. The temperature of volcanic magma eruption is 1200 ℃. When the magma cools to 800-900 ℃, the magma crystallizes and forms columnar joints. Because the magma contains such minerals as plagioclase, olivine, amphibole, pyroxene and so on, the hexagonal column is formed after cooling, which is called columnar joint.

Columnar joint

This entry is compiled and applied by "popular science China" Science Encyclopedia

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Columnar joints are columnar joints formed when volcanic rocks cool down. It is usually found in basic lava and acid lava forming rock mass. The most common joint column is hexagonal or pentagonal. Most joint planes are straight and parallel to each other. The diameter of joint column ranges from several centimeters to several meters. This kind of joint is formed by volume shrinkage of hot lava during rapid cooling. Columnar joints can be found in many geoparks related to volcanic rocks, such as Zhangzhou coastal Volcanic National Geopark (basalt) in Fujian Province and Hong Kong National Geopark (rhyolitic volcanic rock) in China.

Columnar joint structure is a regular or irregular columnar primary tensile fracture structure commonly found in volcanic lava. It is often found in basalt, and sometimes in intermediate acid lava, tuff, subvolcanic rock and basic dikes. The rock mass with columnar joints is usually in the form of tetragonal, pentagonal and hexagonal prism. The more famous one is devil's pillar in eastern California, as shown in the figure.

formation

The dominant theory of the formation mechanism of basalt columnar joints is "cooling shrinkage theory". According to the theory, the ideal way of forming columnar joints in basalt flow is that during the cooling process of the flow, the flat lava condensation surface forms numerous regular and spaced uniform contraction centers, and produces tension cracks perpendicular to the contraction direction. Volume contraction causes the rock material to gather to the fixed internal center, which causes the rock to split and form polyhedral columns. In the ideal case, if the rock is homogeneous, the distance between the contraction centers is equal, and finally presents a hexagonal pattern in the plane. With the continuous cooling and solidification of the magma, the tension cracks form regular hexagonal prism in the direction perpendicular to the condensation surface. In fact, the formation of basalt column is affected by various environmental conditions, especially the heterogeneous structure in the rock mass, so many combinations such as hexagon, quadrilateral and heptagonal are formed on the column section.

give an example

Shenzhu, Tengchong County, Yunnan Province

On the Bank of the Longchuan River in Tengchong County, Yunnan Province, there stands a large area of columnar crystal formed by the condensation of unexposed magma from the eruption. Geologically, it is called "columnar joint", while the local people vividly call it "Shenzhu".

Columnar joints in Shandong Province

This phenomenon is also found in the tuanzishan crater in Changle, Shandong Province, but the scale is not very large, but it is very valuable for geological research.

Tengchong's "God pillar"

Geological experts believe that the "Shenzhu" in Tengchong is the largest, well preserved and the shortest columnar joint discovered so far in China.

Columnar joints in Fujian Province

The columnar joints on Nanding island in Zhangpu County, Zhangzhou City, Fujian Province are also very large in scale and more ornamental than those in Tengchong.

Address: Tengchong Volcanic geothermal National Geopark, Tengchong County, Baoshan City, Yunnan Province

Longitude: 98.568000793457

Latitude: 25.240400314331

Tour time: 1-2 hours

Traffic information: [external traffic]

1. There is a special bus to Tengchong County. The ticket price is 5 yuan per person

2. You can take bus No.6 to the triangle, and then take a minibus to the volcano park. The ticket price is 7 yuan

3. Taxi directly to the park gate, round-trip 60 yuan

Internal transportation

You can take the battery car in the scenic area

Ticket information: included in the ticket of Tengchong volcano geothermal National Geopark

Opening hours: 8:00-18:00