Akan-Mashu National Park: nests of volcanoes and calderas
September 8, 2024
You may have visited Crater Lake, Oregon’s only national park. You may know that it is misnamed. A crater is the depression on the top of a volcano where lava and/or pyroclastic materials spew forth during eruptions. But Crater Lake should actually be called Caldera Lake. Calderas are formed when volcanoes are so explosive that they blow off a major part of their ediface to create a huge depression.
Akan-Mashu National Park is filled with calderas. The park was created in 1934—one of the two oldest parks in Hokkaido. It has long attracted tourists who enjoy the lakes, the views, the hiking, the hot springs, and other amenities. The park is in a straight NE-SW line with Shiretoko National Park, as shown on the map in my previous post: https://landscapes-revealed.net/shiretoko-peninsula-japans-end-of-the-earth/. It is a continuation of the Kuril volcanic arc.
What a landscape! “Crater” Lake is just a single caldera. But in Akan-Mashu National Park, there is a complex network of nested calderas and still-intact volcanoes that have built up into and around the calderas. The three major caldera lakes are labeled in blue, and the volcanoes I’ll refer to in this post are labeled in red. For scale, Lake Kussharo is 20 km (12 miles) wide and 26 km (15.6 miles) long.
Lake / Caldera Kussharo
Lake Kussharo is the largest caldera lake in Japan and one of the largest in the world. Look at the map above. The walls of the caldera, the remaining parts of the original volcanic ediface, are about twice as large as the lake. All of the area around Mt. Io is volcanic material that has been erupted since the caldera was created in a series of major eruptions between about 340,000 and 30,000 years ago.
Many lava domes have formed around the edge of the caldera and in the center, creating an island. Lake Mashu is a younger caldera on the eastern side of Kussharo, with its own set of even younger volcanic buildups. I took the photo from the western edge of the caldera but Mashu was not visible because of the clouds. We then drove south and into the caldera-filled area to check out Mt. Io.Mt. Io (=sulphur mountain) volcano is called “bare mountain” in the Ainu language because the slopes are mostly bare of vegetation due to the volcanic gases. Mt. lo formed around 1,000 years ago in the eastern part of the Kussharo caldera. Upon arriving, we were immediately hit by the strong sulfur odor. As shown in this photo, hot steam escapes through fumaroles (small vents). The nearby Kawayu Onsen (hot springs) originate from Mt. Io’s geothermal activity.A closeup view of the sulphur fumeroles. Jay had to take this photo because my hat so closely matched the color of the sulphur! As at Mt. Iou in Shiretoko National Park, the sulfur from this volcano has been mined for various uses.
Lake / Caldera Mashu—”Crater” Lake’s cousin
Lake Mashu is a smaller caldera that developed on the eastern edge of the Kussharo caldera (see map above). I took this photo from a viewpoint on the western edge of the lake/caldera. With a diameter of 6 km, Lake Mashu is slightly smaller than Oregon’s “Crater” Lake that has a diameter of 8 km. They have many features in common. Because they are both enclosed lakes without river input, they have brilliant blue colors and high water clarity. Unfortunately, on the day we visited it was very cloudy, so these qualities were not so obvious.
The explosive eruption that created Mashu caldera was 7,000 years ago, similar to “Crater” Lake’s 7,700 year age! A resurgent lava dome forms an island in Mashu Lake’s center, much like Wizard Island in “Crater” Lake. A much smaller exploded cone forms a satellite volcano on the eastern edge of Mashu Lake, but it’s not visible in the photo because of the low cloud cover.Also like Oregon’s “Crater” Lake, thick deposits of volcanic ash are visible along roads in the vicinity of the calderas. I don’t know the age of this thick ask deposit, but it is certainly from one of the calderas in this area.
Lake / Caldera Akan
Lake Akan is another large caldera that has filled in with subsequent volcanic eruptions. If you look at the map above, you can see that the caldera walls (24 x 13 km diameter) surround two smaller lakes, Mt. Oakan, Mt. Meaken and other smaller cones. The Akan Volcanic Complex is a group of stratovolcanoes that grew out of the Akan caldera that formed 31,500 years ago. Its elongated shape is due to formation during several major explosive eruptions.
The highest peaks in the complex are the stratovolcanoes Oakan, Meakan, and Akan-Fuji, one of the many symmetrical Japanese volcanoes named after the reknown Mount Fuji. Meakan (sometimes spelled Me-Akan) is one of the most active volcanoes of Hokkaido and in all of Japan. Its summit contains two active craters that are sites of frequent historical phreatic eruptions, the last one in 2008. Geologic studies have demonstrated that at least four major magmatic eruptions with pyroclastic flows occurred during the past 10,000 years.
After a cloudy day during our visits to Kussharo and Mashu, we were fortunate to have a picture-perfect day to climb Mt. Meakan, a truly spectacular volcano to gaze upon. It was located just a short 15-minute drive from our hotel on the edge of Lake Akan.
This main crater of Meakan volcano was formed during a major eruption about 13,500 years ago (view to the south). Notice the fumerole on the other side of the crater, beneath the clouds. The small lake in the center of the crater is yellow because of some sulphur content. After climbing 780 m (2500 ft), we were very happy to reach the summit of Meakan volcano. At 1449 m (4750 ft), it is the tallest mountain in the Akan Volcanic Complex. It is also the most active, but it was serene during our visit except for the sound of various fumeroles venting within the crater.This is an eastward view from the summit of Meakan volcano. In the foreground is a small caldera that formed within the larger Akan caldera. It is white because of hydrothermal activity that leeched volcanic materials and turned them to clay. In the distance is Akan Lake and Oakan volcano on the other side of the lake. Oakan (O-Akan) volcano was frequently active during the last 10,000 years, but no historical eruptions are known. Keep in mind that the native Ainu people had no written language and the Japanese only arrived in the late 1800s. By the way, Meakan and Oakan are considered to be a married couple. This is often the case with two prominent mountains within the same area in Japan.This is a southward view over the second main Meakan crater, with a perfectly-circular green lake at the bottom. The peak next to Meakan is Meakan-Fuji. Notice its perfectly conical shape, which is why it received the “Fuji” name. It is active, but no historical eruptions are known.Left-side photo. Andesite is the dominate rock type in these stratovolcanoes. This rock has an intermediate concentration of silica that is higher than basalt and lower than rhyolite. The white spots are feldspar crystals that form when magma is still underground. When the magma erupts, the lava cools quickly and the remaining crystals are too small to see. The red fragment at my finger tip is a lithic. It is a piece of rock picked up from older volcanic rocks as the magma passed through them before erupting.
You might guess that this is the expected composition in a chain of volcanoes formed by subduction tectonics. Andesite is named for the Andes, which are a long chain of volcanic mountains formed next to the subduction zone extending along the west coast of South America. The most explosive eruptions, however, are typically more silica-rich compositions (e.g., rhyolite) that also tend to have higher gas concentrations.
Right-side photo. This is the north side of Meakan volcano during our climb. The quick-growing vegetation obscures even young volcanic deposits, but note the slope-parallel ridges in the middle green section that retain the flow pattern of lava flows. It was interesting to walk upward through vegetation changes—from tall trees (dark green) to low bushes (middle green) to very short conifers (closest green).
Other features
Lake Akan is known for a rare green algae called marimo that can grow to the size of a soccer ball. We saw these marimo algae balls in the Eco-Center along the edge of the lake. Note Jay’s finger for scale.Left-side photo. With all of the active volcanoes in the Lake Akan area, there are, of course, many onsens (hot springs) and our hotel had a wonderful onsen. The edge of Lake Akan a short distance from our hotel is an active geothermal area where the heat immediately melts any snowfall. At the lakeshore, we saw bokke, which comes from “pofuke”, meaning “bubble up” in the Ainu language. A bokke is a mud volcano, where heated mud erupts continuously from an underground vent along with volcanic gases.
Right-side photo. We were still in brown bear habitat, but fortunately the only bears we saw were in the Eco Center.
Hi Karen. Thompson here in SMP on a cold foggy Sunday morning. Just wanted to say hello to you both and tell you how much I enjoyed this particular blog edition. Love all the Caldera versus crater comparisons particularly to crater Lake, which of course we loved when we visited. Plus you included some fantastic photos! And always jealous of all the amazing traveling you guys are doing in your retirement. Speaking of which, Billy and I are leaving in two weeks for Greece for three weeks. Wondering if you have any fantastic geological sites you might recommend we visit while we’re there. We will be in Athens, Crete, Santorini, Naxos, and then driving up to Meteora. Though I believe our hotel in Fiera Santorini looks out over a caldera. Can’t remember if I’ve read a blog edition involving Greece. Happy travels! T&B
Landscapes Revealedon September 9, 2024 at 5:48 am
Thanks Thompson—so good to hear from you! Remembering how you saw my blog and we realized we were in same place in Spain in 2015 and met for dinner! I have been to Athens and Santorini, but in 1989, long before starting the blog. Santorini is a geologic wonder—you will be on the edge of a REALLY large caldera. That eruption, in 1500 BC, is believed to have ended Minoan civilization (in Crete) and had other big effects. Imagine the tsunami and weather changes that would have resulted from something so huge. You’ll probably visit Akrotiri, the archeological site of a town on Santorini that was buried by volcanic ash during the eruption. That’s all the wisdom I can convey. We plan to go to Cyprus next year and plan to add other places—we may need to ask you about Crete. Safe and happy travels! -K
Karen (and Jay),
What an incredible journey you are having! The pictures and background information are fascinating. You guys take such interesting and enriching trips. Very inspiring.
BTW, I’ve dealt with a lot of algae issues in SF Bay, but never saw big balls like that. Crazy!
Hi Karen. Thompson here in SMP on a cold foggy Sunday morning. Just wanted to say hello to you both and tell you how much I enjoyed this particular blog edition. Love all the Caldera versus crater comparisons particularly to crater Lake, which of course we loved when we visited. Plus you included some fantastic photos! And always jealous of all the amazing traveling you guys are doing in your retirement. Speaking of which, Billy and I are leaving in two weeks for Greece for three weeks. Wondering if you have any fantastic geological sites you might recommend we visit while we’re there. We will be in Athens, Crete, Santorini, Naxos, and then driving up to Meteora. Though I believe our hotel in Fiera Santorini looks out over a caldera. Can’t remember if I’ve read a blog edition involving Greece. Happy travels! T&B
Thanks Thompson—so good to hear from you! Remembering how you saw my blog and we realized we were in same place in Spain in 2015 and met for dinner! I have been to Athens and Santorini, but in 1989, long before starting the blog. Santorini is a geologic wonder—you will be on the edge of a REALLY large caldera. That eruption, in 1500 BC, is believed to have ended Minoan civilization (in Crete) and had other big effects. Imagine the tsunami and weather changes that would have resulted from something so huge. You’ll probably visit Akrotiri, the archeological site of a town on Santorini that was buried by volcanic ash during the eruption. That’s all the wisdom I can convey. We plan to go to Cyprus next year and plan to add other places—we may need to ask you about Crete. Safe and happy travels! -K
Karen (and Jay),
What an incredible journey you are having! The pictures and background information are fascinating. You guys take such interesting and enriching trips. Very inspiring.
BTW, I’ve dealt with a lot of algae issues in SF Bay, but never saw big balls like that. Crazy!
Have a great rest of your trip and keep posting!
– Mark and Lynn
We need to meet you again in one of these interesting places, like we did last September! Thanks for reading!