What Are Hot Springs & How Are They Formed

Kurt Norris
Last Updated: March 7th, 2023

Hot Springs have been engaged as natural sites of healing and rejuvenation for millennia. However, despite their widespread abundance and influence across numerous historical cultures, few know what actually makes a hot spring.

Sure, most people know the basics. A hot spring is a naturally heated thermal pool. And while this is true to an extent, the actual definition of a hot spring is more complex than that, and some experts argue that not all thermal pools are hot springs.

So, for many, this begs the question; What are hot springs, and how are they formed?

What Are Hot Springs?

Maruia Hot Springs Via LuxTonnerre

While hot springs are celebrated worldwide, there is no definitive definition of what comprises a hot spring. As a result, hot springs come in several different forms and temperatures, each providing a unique soaking experience.

Most people agree that to be considered an actual hot spring, a natural mineral spring must be geothermally heated to temperatures sustainably higher than its surrounding environment’s.

However, these exact temperatures vary between sources, with some claiming the pool must feature temperatures above the human body temperature. In contrast, others argue that a hot spring is any thermal pool with temperatures above 70 degrees Fahrenheit.

For this reason, thermal pools are classified into various categories depending on their mineral compositions and average temperatures. The most traditional form of hot springs is those with average temperatures averaging at or above 95 degrees Fahrenheit.

The Key Geothermal Features of a Hot Spring


While the exact characteristics that define a hot spring are universally debated, most people agree that a thermal pool must at least boast these four required features to be considered a hot spring.

  • The Water Source: To be considered a hot spring, a thermal pool must be filled by a natural source originating from the earth’s surface. The spring can derive from rainwater, snowmelt, or even an underground spring or aquifer, but it cannot be artificially filled to be considered a natural hot spring.
  • A Heat Source: Similarly, natural geothermal processes must also heat a hot spring. This typically happens as the water passes through the earth’s crust and can be caused by several factors, including tectonic movements, radioactive decay of minerals, and volcanic activity.
  • Temperature: While the exact temperature threshold of what comprises a hot spring is debated, it is generally accepted that a thermal pool must at least be sustainably warmer than its surrounding environment to be considered a natural occurrence.
  • Mineral Content: Due to the spring’s natural process and movements through the earth’s surface, a hot spring typically boasts high mineral concentrations that grant its therapeutic properties. However, exact mineral compositions vary between pools, and as a result, every hot spring provides a unique soaking experience with varying health benefits.

How are Hot Springs Formed?


Formed over thousands of years, hot springs have been popular centers of healing and rejuvenation among various populations and cultures for centuries. However, until only recently, these naturally heated thermal pools were a largely inexplicable phenomenon.

While today we know that hot springs are formed by natural geological processes beneath the earth’s surface, these naturally heated waters were once attributed to various gods and miracles, with several global cultures deriving mythological origins describing the occurrence.

Nevertheless, today we know that a natural hot spring is formed out of nothing more than the planet’s geological processes. Although, this doesn’t mean that thermal pools are any less wondrous.

Deriving from rainwater, snowfall, or any other natural source, a hot spring is formed when water percolates its way through the earth’s surface. As it travels deeper into the earth’s crust, the water is heated thanks to geothermal processes such as tectonic movements, volcanism, or the radioactive decay of minerals.

Eventually, as the water begins to hit elevated temperatures, it shoots back towards the earth’s surface through cracks and fissures until it is excreted into a natural thermal pool on the planet’s surface.

Throughout its journey through the earth’s inner layers, the natural spring absorbs the various minerals of the region. As a result, every spring boasts its own mineral composition and offers a unique soaking experience with varying therapeutic and curative properties.

The Different Types of Hot Springs

No two thermal pools are the same. And while there are several types of hot springs worldwide, most can typically be classified as one of the following categories depending on average temperatures and chemical compositions.

Soaking Pools


Not all hot springs are safe to submerge in, thanks to either unbearable temperatures or acidic chemicals. However, those that people are allowed to swim in are often marked as Soaking Pools.

These safe-to-interact-with pools typically feature temperatures of 104 degrees Fahrenheit or below, but they can also include slightly warmer pools reaching up to 115 degrees. It is critical to remember that the warmer a pool is, the shorter a session should be.

Warm Springs

While technically a soaking pool, a warm spring is a natural thermal swimming hole that features temperatures slightly cooler than a traditional hot spring. While the term is refuted by some that argue that a pool requires a lower temperature to be considered a hot spring, a warm spring is typically considered a thermal pool averaging between 65 and 95 degrees Fahrenheit.

While not as hot as a soaking pool, these warm pools are often some of the most popular geothermal springs among visitors and offer family-friendly swimming experiences in comfortable water temperatures.

Hot Pools

Unfortunately, not all hot springs are submersible. Some hot springs are far too hot for the human body to bear, and any hot springs that exceed 115 degrees Fahrenheit is considered a hot pool.

While visitors may be unable to swim directly in these natural springs, these pools are often some of the most beautiful to observe and can often offer a nearby bathhouse that cools the waters to more bearable temperatures. Arkansas’ Hot Springs National Park is home to the most famous examples of these exceedingly hot springs.


A geyser is a distinctive hot spring that occurs only when a restrictive pathway contains a thermal pool. Blocked from excreting out of the earth, the spring water is continuously heated until it reaches boiling point, at which point it forces its way through the geyser and shoots several feet into the air.

While geysers are found all over the world, the most famous are the ones in Yellowstone National Park, including the universally recognized Old Faithful Geyser.

Natural Mud baths

Also known as a mud pot, a mud bath, as the name suggests, occurs when a natural hot spring mixes with dirt or clay before reaching the earth’s surface. Most mud baths are unsafe to enter and typically feature boiling temperatures and high acidities.

However, those that are safe to submerge in feature cooler, more comfortable temperatures and boast high mineral concentration for an even more, enhance therapeutic soak.

About The Author

Kurt Norris

A Canada-based freelance writer, Kurt acquired his bachelor’s degree in English Language and Literature from the University of Windsor. He began his professional writing career while in school as a sports journalist. Upon graduating, Kurt left the courtside media desk behind and began venturing the globe. Throughout his journeys, Kurt enjoys partaking in slow travel and loves to explore the histories and cultures of each destination, which he shares with others through his writing.

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