Gifts from the Deep Earth: Why are hot springs hot? What other uses does geothermal energy have?

Produced by: Science Popularization China

Author: Wang Huiqi (Institute of Deep Sea Science and Engineering, Chinese Academy of Sciences)

Producer: China Science Expo

Editor's note: In order to expand the boundaries of cognition, the China Science Popularization Frontier Science Project has launched a series of articles on the "Unknown Realm", which provides an overview of the exploration results that break through the limits in deep space, deep earth, deep sea and other fields. Let us embark on a journey of scientific discovery and get to know the amazing world.

On this planet, nature has created a treasure trove of magnificent scenery and endless mysteries for us to appreciate and explore. Among them, hot springs, as a treasure of nature, not only soothe the body and mind and rejuvenate, but also contain rich geothermal energy. Here, the miracles of nature and the wisdom of mankind complement each other, leading us on a journey of exploration full of surprises.

(Photo source: veer photo gallery)

The Geology Behind the Hot Springs

The formation and distribution of hot springs is a complex natural process that integrates the influence of many factors, including the heat source inside the earth, geological tectonic activities and climatic conditions.

These natural hot springs are like messengers from the underworld, quietly emerging from the depths of the earth's crust and starting a magical underground journey . Initially, water molecules from the atmosphere quietly penetrate into the porous rocks underground in the form of rain or snowmelt. As the depth increases, these water molecules gradually sink deep into the earth. In this process, they are heated by the high temperature from the mantle, and the temperature of the mantle is raised by the huge heat inside the earth.

This heat mainly comes from two aspects: one is the original heat energy remaining in the earth's early formation; the other is the heat released by the earth's internal materials during chemical reactions and radioactive decay. This heat is continuously transferred to the circulating groundwater, causing its temperature to gradually rise.

Eventually, when this geothermally heated water encounters cracks or faults in the Earth's crust, it will rise along these channels and eventually surge to the surface; or it will erupt through plate tectonic movement accompanied by volcanic activity, such as the Pacific Ring of Fire, which is rich in hot springs due to its proximity to geological fault lines and volcanic activity. This journey upward through the rock layers can take years or even centuries. During this process, the water reacts with the surrounding rocks and absorbs a variety of minerals, such as calcium, magnesium, and sulfur. Finally, it appears on the surface in the form of hot springs - a vivid demonstration of the Earth's geothermal energy and geological diversity.

(Photo source: veer photo gallery)

In China, the distribution of hot springs is mainly affected by geological structures. High-temperature geothermal activity areas are mainly distributed near plate boundaries such as Tibet and Yunnan in southwest China and Taiwan. These areas may have young magmatic activities, providing heat sources for geothermal activities. In inland China, geothermal activities are mainly formed along the deep circulation of fault zones. These fault zones provide rising channels for deep groundwater, allowing geothermal heat to be smoothly conducted to the surface and form hot springs. In addition, climatic conditions also have an important impact on hot springs and geothermal water. The amount and intensity of precipitation are directly related to the circulation and replenishment of hot spring geothermal water.

There are many ways to classify hot springs, and so far, there is no unified classification standard in the world. Hot springs can usually be classified according to the content of dissolved mineral elements, temperature, source discharge (flow rate) or pH value (acidic, neutral, alkaline), or they can be classified based on chemical composition, geology, physical properties, etc.

According to the classification of chemical composition, hot springs can be divided into four main types: chloride springs, bicarbonate springs, sulfate springs and mixed springs; from a geological perspective, hot springs can be divided into igneous rock area hot springs, metamorphic rock area hot springs, sedimentary rock area hot springs, etc.; according to the water temperature, they can be divided into cold springs, hot springs, hot springs and superhot springs.

In addition, more types can be further subdivided according to the pH, osmotic pressure, etc., such as simple hot springs, sodium bicarbonate springs, sodium salt springs, carbon dioxide springs, calcium magnesium bicarbonate springs, sulfate springs, iron-rich springs, hydrogen sulfide springs (sulfur springs), etc.; according to the activity type, form and other physical properties of the hot springs, hot springs can also be divided into ordinary hot springs, intermittent hot springs, boiling springs, fountains, fumaroles (or sulfur pores), hot mud springs, etc.

Protection and sustainable development of hot springs

Hot springs not only carry the value of entertainment and healing, but also show great potential as a renewable energy source . Geothermal power plants cleverly utilize underground heat energy, not only providing us with electricity and heating, but also reducing our dependence on fossil fuels to a certain extent, making important contributions to mitigating climate change and protecting the earth's environment.

Hot springs are natural signs of geothermal activity and a direct display of the Earth's internal structure and geological activity. By studying hot springs, we can gain a deeper understanding of the Earth's internal structure, geological changes, and the distribution and reserves of geothermal resources, which is of great significance for promoting geological science research and resource exploration and development.

However, current research on the sustainable development and microbial diversity of hot springs is still insufficient. The microbial community in hot springs is also a complex and unique ecosystem, which is of great significance for maintaining the ecological balance and biodiversity of hot springs.

As the popularity of hot spring tourism continues to rise, we should implement sustainable management measures to prevent ecological damage caused by over-exploitation, such as resource pollution and ground collapse. Therefore, only by continuously exploring the mysteries of hot springs, strengthening scientific research and monitoring of hot spring resources, and formulating scientific and reasonable development and protection strategies, can we use these geothermal resources to rationally develop and utilize clean renewable energy, reduce carbon emissions, and make hot springs continue to be a green paradise for the coexistence of humans and wild animals and plants.

(Photo source: veer photo gallery)

In the embrace of the vast mountains, there is a little-known secret oasis. There, a pool of hot spring water is like a gift from the ancient gods, offering a healing kiss of nature to every seeker. This is not just a clear spring, it contains thousands of years of wisdom and energy, not only soothing people's bodies, but also allowing people to feel the wonder and beauty of life in this tranquility and harmony. Hot springs are not just a natural landscape, but also a holy place full of wisdom and enlightenment.

A natural hot spring spot to be developed in Hongxie Village, Yingzhou Town, Lingshui Li Autonomous County, Hainan Province

Image credit: Li Guili (Institute of Deep Sea Science and Engineering, Chinese Academy of Sciences)

References

[1] Yu Wei. Research on planning methods of hot spring resorts[D]. Tongji University, 2008.

[2] Formation of hot springs[J]. Western Resources, 2011, (3): 45-45.

[3] Liao Zhijie. China's volcanoes, hot springs and geothermal energy[M]. China International Broadcasting Press, 2012.