China's southernmost tropical city volcano group is wearing a pair of "sunglasses"! Don't believe it? Look!

Leizhou Peninsula is the third largest peninsula in my country. It is located at the southernmost tip of the mainland of China. It has a superior location and is located at the intersection of Guangdong, Hainan and Guangxi provinces (regions). It is named because it was historically under the jurisdiction of Leizhou. Together with Shandong Peninsula and Liaodong Peninsula, it is known as the three major peninsulas in China. Hainan Province, referred to as "Qiong", is located at the southernmost tip of China and is a provincial-level administrative region in my country. The abbreviation "Qiong" of Hainan Province comes from the historical Qiongshan County, and Qiongshan County is named after a hill called "Qiongshan".

The Leizhou-Qiong area of ​​my country is located in the southwest of Guangdong Province, including the Leizhou Peninsula of Guangdong Province, the northern part of Hainan Island and the Qiongzhou Strait, with an area of ​​about 17,500 square kilometers, of which the land area is about 13,000 square kilometers. Its civilization history can be traced back to more than 3,000 years ago. The Leizhou-Qiong area was once a whole, and it experienced extension, rifting, sea level rise and fall, land-island separation and the Quaternary Ice Age, and finally formed the Leizhou-Qiong volcano group across the strait today.

The Leiqiong (Leizhou Peninsula and northern Hainan Island) volcanic group is the southernmost volcanic group in mainland China. About 177 Cenozoic volcanoes have been discovered. The volcanic activity is mainly fissure-type eruption, and there are also central eruptions. The activity of the volcanic group lasted from the Middle Cretaceous to the Holocene: the southwestern part of the South China Sea began to expand during the Middle Cretaceous, resulting in the initial formation of the Leiqiong Rift Valley, and volcanic activity occurred locally in the region; from the Oligocene to the Miocene, the expansion of the South China Sea caused the Leiqiong Rift Valley to continue to rift and collapse, resulting in crust thinning, and the upper mantle material overflowed along the fault to form volcanic eruptions; in the Middle Pleistocene, the Leiqiong volcanic activity gradually reached its peak; by the Holocene, the Leiqiong volcanic activity tended to be calm. The most recent eruption was in the Shishan area of ​​Hainan Island, about 8,000 years ago. The volcanic rocks are mostly quartz tholeiitic basalts and olive tholeiitic basalts, and a small amount of alkaline basalts also appear in some areas. Some alkaline basalts also carry mantle peridotite inclusions and monoclinic pyroxene and garnet megacrystals. The activities of the regional volcanoes are jointly affected by the collision of multiple plates and the upwelling of mantle plumes. In September 2006, Leiqiong Geopark was awarded the title of "World Geopark" by UNESCO.

Location map of some volcanoes in the Leizhou Peninsula volcanic group in Guangdong Province (left) and location map of some volcanoes in the Qiongbei volcanic group in Hainan Province (right) (both images are from GF-2 Earth observation images and the National Geographic Information Public Service Platform)

The volcanic rock area in the Leiqiong volcanic area is about 8,000 square kilometers, of which about 3,900 square kilometers are in the Leizhou Peninsula and about 4,100 square kilometers are in the northern part of Hainan Island. Except for a very small number of Paleogene and Neogene volcanic rocks, the rest are Quaternary volcanic rocks. Among them, the volcanic landforms in the northern part of the Leizhou Peninsula are generally well preserved, such as the Huguangyan volcano, the Naozhou Island volcano (also known as the Dengta volcano), the Weizhou Island volcano, etc. The volcanic eruptive rock types are mainly basaltic volcanic rocks. Today, the Leiqiong volcanic group has become the volcanic group with the largest distribution area and the largest number of volcanoes among the Quaternary volcanoes in China, and it is also the only tropical urban volcanic group world geological park. Among them, the low-lying crater lake (Maar Lake) formed after the eruption of the Huguangyan volcano in the north of the Leizhou Peninsula signed a "Sino-German Sister Lake" cooperation agreement with the Maar Lake in the Eiffel region of Germany. If the Huguangyan Maar Lake is picturesque and famous both at home and abroad, then the Maar Lakes distributed within the Longgang Volcanic Group in Jilin Province have a different kind of majestic atmosphere and breathtaking beauty!

The Qiongbei volcanic group is located in the northern part of Hainan Island. It is an important part of the Leiqiong volcanic group and also an urban volcanic group. The Qiongbei area is also one of the areas with major historical earthquake activity in my country. There are more than 140 identifiable craters preserved in the Qiongbei volcanic group, and the volcanic lava covers an area of ​​about 4,000 square kilometers, covering seven cities and counties in Hainan Province, including Haikou, Chengmai, Lingao, Danzhou, Ding'an, Wenchang and Qionghai. The volcanic group is regularly arranged in a northwest direction, all located on the north side of the Wangwu-Wenjiao fault zone. Most of the volcanic cones are well preserved, and the crater outlines are clear. Quaternary volcanic rocks are the most widely distributed volcanic rocks in the Qiongbei volcanic area. Most of them are exposed on the surface and form large areas of basalt and numerous volcanic cones. Among them, many active volcanoes such as Leihuling Volcano and Ma'anling Volcano are active volcanoes that have erupted in the Holocene for about 10,000 years. If the rope-shaped, twisted and coral-shaped basaltic lava flows in the northern Qiongshan volcanic area are absolutely beautiful, then the basaltic lava flows of the Tianchi volcano in Changbai Mountain, Jilin Province are even more brilliant!

Location map of Huguangyan Volcano in Leizhou Peninsula Volcanic Group (left), Fengluling Volcano in Qiongbei Volcanic Group (middle) and Yanjingling Volcano (right) (all pictures are from the Internet)

The low-lying crater lake (Maar Lake) of Sanjiaolongwan Volcano in Jilin Province (left picture from the Internet) and the low-lying crater lake (Maar Lake) of Nanlongwan Volcano (right picture, original picture)

Basaltic lava in the Qiongbei volcanic area (left and middle) and basaltic lava in the Tianchi volcanic area of ​​Changbai Mountain in Jilin Province (right) (both original images)

The Ma'anling volcano (group) is located about 15 kilometers southwest of Haikou City. There is a "V"-shaped gap in the northeast of the crater, which was the outlet of the lava flow from the volcanic eruption at that time. The Ma'anling volcano is composed of four volcanoes, the southern cone Fengluling volcano, the northern cone Baoziling volcano and two parasitic small volcanoes on the side. From a distance, the outline of its composition resembles a saddle. The southern cone volcano is larger in scale and looks like a wind furnace. It was called Fengluling in ancient times and is now renamed Fengluling volcano. The Fengluling volcano is about 222.8 meters in height, with a circular base and an inner diameter of about 120 meters. The two parasitic volcanoes next to the Fengluling volcano are like Fengluling volcano wearing a pair of glasses, and are called Glasses Ridge volcanoes. The one on the east is mainly jet-fueled, and the one on the west has lava overflowed. Looking down at the thick outline of the crater, it looks more like a pair of sunglasses. So, the volcanic group in the southernmost tropical city in China is wearing a pair of "sunglasses", and the "glasses degree" is different! In addition, the Ma'anling volcano (group) erupted more than 8,000 years ago and is also the youngest volcano in the Leiqiong World Geopark.

The volcanic landforms formed by the eruption of Ma'anling Volcano, such as craters, volcanic cones, surface lava flows and underground lava tunnels, are of various shapes. The rainforest plank roads, Chinese fuchsia trees, lychee trees, Hainan huanghuali trees and frangipani trees formed in the volcanic area are like furry green clothes draped over the volcanic group, fully demonstrating the beauty of volcanic ecological culture. Ma'anling Volcano was formed by multiple eruptions of magma, and parasitic volcanic cones are many small volcanic cones formed on the hillsides around the main volcanic cone after the formation of the main volcanic cone, while volcanic activity is still going on. This kind of parasitic volcanic cone is a relatively common volcanic geological phenomenon worldwide. For example, there are more than 300 parasitic volcanic cones on the large active volcano Etna in Catania, Italy.

The parasitic cones on the north slope of the large active volcano Etna in Catania, Italy (left, original image) and the parasitic cones on the east slope (right, original image)

Leihuling Volcano is located about 4 kilometers southeast of Yongxing Town, Haikou City. The volcano is named after its crouching tiger shape. The crater is nearly twice as large as the Ma'anling crater, making it more majestic. The volcano is about 168 meters above sea level, with a slope of about 30°. The diameter of the crater is about 280 meters, the bottom diameter is within the range of 50-100 meters, the inner slope is about 50°, and there is a gap in the northeast. The crater wall is stepped, and the bottom is wide and flat, resembling a giant natural stadium. According to the historical data "Lingao County Chronicles", "In the ninth year of Guangxu (1883), the ground in Lingao cracked, and there was fire, and the grass and trees turned into ashes, and the soil was as black as ink." Before liberation, Guangzhou's Yuehua Newspaper also reported: "In late June 1933, a fire broke out on Nanshe Ridge, about 30 miles away from Jinjiang City in Chengmai County. It was more than ten feet long and dazzling, and looked like a fire dragon from a distance. On July 7, a hurricane arose, and the next day the ridge suddenly exploded at the fire, and the huge rocks on the top of the ridge collapsed and fell, crushing more than 20 acres of land..." It is generally believed that the fire came first and the explosion came later, suspected to be a volcanic eruption, and there are volcanoes distributed in Lingao and Chengmai counties on Hainan Island. Therefore, the above historical records can show that the Qiongbei volcano group is still active in modern times.

In addition, volcanic observation and research data of the Qiongbei volcanic group show that about 32 hot springs have been identified in the volcanic area, and the released volcanic gases include H2O, Rn, He, CO2 and CH4, which are mainly of crustal origin and mixed with a small amount of mantle-derived components. Seismic background noise imaging in the volcanic area shows that there are magma chambers in the upper crust within 5-15 kilometers at the bottom of the volcanic group. Existing seismic monitoring data in the volcanic area show that earthquakes in the volcanic area are mainly micro-earthquakes, with occasional felt earthquakes. Among them, about 151 earthquakes above ML1.0 were recorded in the volcanic area from 1998 to 2021, with the largest earthquake magnitude of 3.5, all of which were tectonic earthquakes (data from the Institute of Volcanology, China Earthquake Administration, Hainan Provincial Seismological Bureau and Guangdong Provincial Seismological Bureau). The above evidence also shows that the Qiongbei volcanic group is still active today.

Volcanic eruption is a natural phenomenon. Volcanoes are divided into active volcanoes and extinct volcanoes. Active volcanoes include volcanoes that are currently erupting and dormant volcanoes that may erupt in the future. Extinct volcanoes refer to volcanoes that have erupted in prehistoric times, but have never been active or have not erupted for a long time in human history. Such volcanoes have lost their ability to move due to long-term non-eruption. The above classification according to volcanic activity is relative, because the fact that many volcanoes have erupted in the past shows that some extinct volcanoes that were originally identified can also erupt suddenly and may cause huge volcanic disasters. For example, the large volcano Vesuvius in Naples, Italy (full name Suma-Vesuvius). In the early BC, the famous geographer Strabo determined that it was an extinct volcano based on the topographical features of Mount Vesuvius. People at that time fully believed this argument. No one expected that it would suddenly erupt on August 24, 79 AD, causing a very serious volcanic disaster.

The huge amount of volcanic ash and high-temperature pyroclastic flows formed by the volcanic eruption engulfed Pompeii, the second largest city in ancient Rome, in a very short time. It was not until the middle of the 18th century that archaeologists excavated Pompeii from several meters of volcanic ash, pyroclastics and other volcanic eruption products. The ancient buildings in the city and the remains of citizens in various postures are well preserved. Today, Pompeii has become a world-famous volcanic relic tourist destination. Today, Mount Vesuvius has been listed by volcanologists as a typical large active volcano in the world, and its eruption danger is slightly less than that of Campi Flegrei, the most dangerous super-active volcano in Europe.

The highest point of the large active volcano Vesuvius in Naples, Italy (left, original image) and the excavated and restored ancient city of Pompeii (center and right, original images)

This issue of science popularization ends! Friends, see you next time!

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Author of this issue: Xu Zhitao, PhD, Institute of Volcanology, China Earthquake Administration, Jilin Province Earthquake Bureau

Ye Xiqing, Institute of Volcanology, China Earthquake Administration, Assistant Engineer, Jilin Province Earthquake Bureau

Sun Liying, Assistant Engineer, Jilin Earthquake Station, Jilin Province Earthquake Bureau

Sveva·R·M PhD, University of Florence, Vesuvius Observatory, Naples, Italy

Stefano C. Senior Researcher, Vesuvius Observatory, Naples, Italy

Vito Z, PhD, Etna Observatory, Catania, Italy

Salvotore G. Senior Researcher at the Etna Observatory in Catania, Italy

Xu Yueren, Researcher at the Institute of Forecasting, China Earthquake Administration

Zhang Xin Guangdong Provincial Earthquake Administration PhD, University of Science and Technology of China

Xu Zhikai, Postdoctoral Fellow, Institute of Oceanology, Chinese Academy of Sciences

Liu Chaoyang Postdoctoral Fellow, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences

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