In Beppu Onsen, a staggering 137,000 liters of hot spring water gushes out every minute. This amounts to approximately 200,000 tons per day. This immense volume continues to flow day after day.

Across Japan, hot spring areas boast incredible amounts of hot spring water. Why does such a large volume of hot spring water emerge? Why doesn't it run dry? Let's delve into these secrets.

What is Hot Spring Output?

Hot spring output refers to the volume of hot spring water that emerges per minute. The unit is "liters/minute" or "kiloliters/minute."

The greater the output, the more abundant the hot springs you can enjoy. This often results in more onsen (hot springs) that offer "gensen kakenagashi" (natural flow from the source).

Japan's Hot Spring Output Rankings

Where in Japan has the highest hot spring output? Let's introduce the top 5.

1st Place: Beppu Onsen (Oita Prefecture)

Output: Approximately 137,000 liters/minute (Japan's highest)

Beppu Onsen has the highest hot spring output in Japan. There are about 2,300 hot spring sources within Beppu City, symbolizing "Onsen Prefecture Oita."

2nd Place: Yufuin Onsen (Oita Prefecture)

Output: Approximately 86,000 liters/minute

Yufuin Onsen, also in Oita Prefecture, is popular as a quiet and serene hot spring area, yet it ranks second in Japan for output.

3rd Place: Kusatsu Onsen (Gunma Prefecture)

Output: Approximately 32,300 liters/minute

Kusatsu Onsen is one of Japan's three famous hot springs. It is said to have the highest "natural output" in Japan. The amount that naturally emerges without pumping is the largest.

4th Place: Dogo Onsen (Ehime Prefecture)

Output: Approximately 20,000 liters/minute

Dogo Onsen is one of Japan's three ancient hot springs. Despite its 3,000-year history, it still boasts a rich output.

5th Place: Noboribetsu Onsen (Hokkaido)

Output: Approximately 10,000 liters/minute

Noboribetsu Onsen offers nine types of spring qualities and has a generous output.

Natural Eruption and Powered Pumping

There are two methods for hot spring output.

Natural Eruption: Hot springs that naturally emerge without pumps.

Powered Pumping: Hot springs that are pumped up from underground.

Kusatsu Onsen has the highest natural output in Japan. Without pumps, 32,300 liters emerge every minute. This is an astonishing figure.

Why Does Such a Large Volume of Hot Spring Water Emerge?

The reasons for the large volume of hot spring water are volcanic activity and geology.

Volcanic Activity

Beneath volcanoes lies magma. This magma heats underground water. The heated underground water increases in pressure and erupts to the surface.

Beppu Onsen, Kusatsu Onsen, and Noboribetsu Onsen, all with high outputs, are located near volcanoes.

Geology

For hot springs to emerge, there must be sufficient underground water. Rainwater and snowmelt permeate underground. This is the source of hot springs.

Japan has abundant rainfall, leading to rich underground water. This is also one of the reasons hot springs emerge.

Output and Gensen Kakenagashi

In areas with high hot spring output, many onsen offer "gensen kakenagashi."

Gensen kakenagashi means that the hot spring water that emerges is directly channeled into the bath, constantly supplying fresh hot spring water. It is not recirculated, diluted, or heated (or minimally).

This is the most luxurious way to enjoy hot springs.

In Kusatsu Onsen, most facilities offer gensen kakenagashi. This is possible because of the 32,300 liters per minute output.

What About Hot Springs with Low Output?

Conversely, some hot springs have low output.

In hot springs with low output, the recirculating filtration method is often adopted. Used hot spring water is filtered and returned to the bath.

This is a method to effectively utilize limited hot spring water. It is not "bad" per se, but compared to gensen kakenagashi, it lacks freshness.

Do Hot Springs Run Dry?

One might wonder, "With such a large volume of hot spring water emerging, won't it run dry?"

In fact, hot springs can run dry. This occurs when excessive pumping depletes the underground water.

However, naturally erupting hot springs are less likely to run dry. Rainwater and snowmelt constantly replenish the underground, and as long as volcanic activity continues, hot springs will continue to emerge.

Kusatsu Onsen has been flowing for over 1,000 years and will likely continue to do so.

Efforts to Preserve Output

Hot spring areas are taking measures to preserve output.

Drilling Restrictions: Limiting the drilling of new hot spring wells.

Pumping Management: Managing the amount of water pumped in powered pumping hot springs.

Environmental Protection: Protecting forests and promoting the recharge of underground water.

Through these efforts, Japan's hot springs are being preserved.

Choosing Hot Springs by Output

Visiting hot spring areas with high output allows you to enjoy abundant gensen kakenagashi.

Beppu Onsen, Yufuin Onsen, Kusatsu Onsen, Dogo Onsen, and Noboribetsu Onsen. These hot spring areas have high output and abundant gensen kakenagashi facilities.

If you want to experience "authentic hot springs," choose areas with high output.

Conclusion

Japan's hot springs boast world-class output. Beppu Onsen produces 137,000 liters per minute, and Kusatsu Onsen produces 32,300 liters per minute (the highest natural output in Japan).

Volcanic activity and abundant underground water create large volumes of hot springs. In areas with high output, you can enjoy luxurious gensen kakenagashi.

Hot springs are constantly replenished by rainwater and snowmelt. With proper management, hot springs will continue to flow without running dry. Japan's hot springs are an eternal gift from the earth.