Hello, this is Takezawa.
Continuing our series on learning about Mount Fuji, today we’ll delve into the “Fuji Five Lakes.”
The Fuji Five Lakes refer to the five lakes: Lake Yamanaka, Lake Kawaguchi, Lake Saiko, Lake Shōji, and Lake Motosu. All of these are part of the World Heritage site encompassing Mount Fuji. However, while Lake Yamanaka and Lake Kawaguchi are registered as independent components, the other three—Lake Sai, Lake Motosu, and Lake Shōji—are included as part of the larger Mount Fuji area. The reasons for this distinction are intriguing and warrant further exploration at another time.
The name “Fuji Five Lakes” was coined relatively recently by Ryōhei Horiuchi, the founder of the Fuji Kyuko Railway. It seems he intended to promote this area as a unified tourist destination—a strategy that has proven successful. In the past, during the era when Fuji-ko (a religious practice centered on Mount Fuji) was prevalent, there was a term “Fuji Eight Seas,” which referred to pilgrimage sites including the Fuji Five Lakes along with Shibire Lake, Asumi Lake, and either Senzu Lake or Sudo Lake.
Now, let’s explore the origins of the Fuji Five Lakes.
Historically, the three lakes—Lake Motosu, Lake Shōji, and Lake Sai—were once a single body of water known as “Se no Umi.” Similarly, Lake Yamanaka, along with the Oshino Hakkai area in Oshino Village, was part of a larger lake called “Lake Utsu.
” It’s worth noting that some academic theories suggest that Lake Utsu may not have existed.
As the New Fuji Volcano began its activity, lava flows blocked existing rivers, leading to the formation of Lake Kawaguchi. The lava that flowed into Se no Umi divided it, resulting in the creation of Lake Motosu. In the year 800 AD, the Enryaku eruption’s lava flow further divided Lake Utsu or the Katsura River, giving birth to Lake Yamanaka. Later, in 864 AD, the Jōgan eruption—the largest recorded eruption—caused lava to fill Se no Umi, leading to the formation of Lake Shōji and Lake Sai.
Interestingly, Lake Motosu, Lake Shōji, and Lake Sai all share the same water surface elevation of 902 meters. This suggests that they were once part of a single lake, Se no Umi. There’s also a phenomenon where, during heavy rainfall, if one lake’s water level rises, the others experience an increase as well, even without direct rainfall. This has led to the “subterranean connection theory,” proposing that the three lakes are connected underground.
A few years ago, NHK aired a program investigating this, but definitive evidence supporting the subterranean connection theory has yet to be found. However, future discoveries might reveal underground tunnels linking these lakes.
Regarding Lake Utsu, past theories have been revised or overturned by subsequent research. While such theories may change over time, they often serve as a gateway to deeper interest and understanding. In this blog, we’ll explore both established and evolving theories to enhance our learning.
The Fuji Five Lakes are all “dammed lakes,” formed by lava flows from Mount Fuji’s eruptions blocking valleys between the mountain and the Misaka Mountain Range to the north. Among them, only Lake Yamanaka has a natural outflowing river, the Katsura River. In the past, the other lakes lacked natural drainage, leading to frequent flooding during heavy rains. However, since the Edo period, the construction of drainage channels has mitigated significant flood damage.
Additionally, southeast of Lake Shōji lies “Akaike,” known as the “phantom lake” or the “sixth lake of Fuji.” This area is usually a grass-covered wetland, but during heavy rains, it’s said that increased water from Lake Shōji seeps through the groundwater, causing Akaike to reappear—a true phantom lake. Notably, in 2011, Akaike resurfaced, drawing attention. While it was reportedly a common sight in the past, it’s unclear when and why it ceased to appear regularly. One theory suggests that the phenomenon diminished about 50 years ago when water from Lake Motosu and Lake Sai, believed to be connected underground to Lake Shōji, began being diverted for hydroelectric power. Here again, the subterranean connection theory comes into play.
So far, we’ve explored the Fuji Five Lakes as a whole. In future posts, we’ll delve into each lake individually to learn more about their unique characteristics.
