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Toya-Usu UNESCO Global Geopark

1.Toya-Usu UNESCO Global Geopark[1]

A geopark where visitors enjoy nature, culture, food and the awesome power of volcanoes

The Toya-Usu UNESCO Global Geopark is a geopark with Lake Toya at its center. Look for the donut shape on a map of Hokkaido. You’ll find a donut-shaped lake (10 km in diameter) in southwestern Hokkaido. This is Lake Toya. Surrounded by mountains, the lake resembles a large pot. Approximately 110,000 years ago, an eruption caused a huge depression to form, and the lake formed when the depression filled with precipitation. Such a lake is called a caldera lake.
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At the center of Lake Toya is an uninhabited island called Nakajima, which consists of several large and small hills. Nakajima Island was also shaped by repeated eruptions approximately 50,000 years ago. The differently shaped hills are the lava domes that formed when lava pushed up from underground.

History of Toya Caldera and Usu Volcano
About 110000 years ago: Occurrence of a massive pyroclastic flow and formation of Toya caldera and lake Toya. It took a long period of time for the depression to be filled with precipitation.
About 50000 years ago: Formation of Nakajima island(domes)
About 20000 years ago: Birth of Mt. Usu stratovolcano
About 10000 years ago: Collapse forming debris avalanche deposit. Mt.Usu lost its summit and entered into a period of dormancy.
About 10000 years ago: People around Lake Toya used stone tools. The Jomon culture thrived. Villages and shell mounds were formed. The Ainu culture thrived
1663: Reawakening & Large eruption; Some casualties.
1769: Pyroclastic flow eruption made several houses burned. The birth of Ogariyama cryptodome.
1822: Major pyroclastic flow eruption with 103 casualties, settlement relocated.
1853: Pyroclastic flow eruption caused the birth of O-Usu lava dome. Residents evacuated.
1910: Eruption at the northwestern flank. The birth of Meiji-Shinzan cryptodome. Successful evacuation, initiation of modern volcanology by Prof. Omori => 1 casualty from hot lahar.
1943-45: Eruption at the eastern flank >The birth of Showa-Shinzan lava dome. >Mimatsu diagram >1 casualty from ash fall.
1977-78: Eruption at summit >Birth of Usu-Shinzan cryptodome >3 casualties from lahar.
2000: Eruption at the western flank >The birth of 2000 Shinzan. >No injuries or casualties due to successful evacuation.
South of Lake Toya is Mt. Usu, an active volcano. Its fumarolic gas, bare rock and awesome traces of eruptions convey the might of the volcano. Mt. Usu has erupted at least nine times since 1663 – four times in the 20th century alone (1910, 1944 – 1945, 1977 – 1978, 2000). Near the summit and the base, visitors can see the many craters that have formed from the repeated eruptions. The most notable characteristic of the Toya-Usu Unesco Global Geopark lies in the fact that people have been living in the shadow of this active volcano. From time to time, craters and faults would form in the town and new hills would be created. Eruptions have caused various disasters and have affected people’s lives. To keep the memories of these disasters from fading, buildings and roads damaged by eruptions have been protected as disaster traces, and a walking path has been built to give visitors access to these.
The 2000 Eruption
This eruption occurred at the foot of the mountain. Despite the proximity to a national route and houses, there were no direct casualties. The early detection of eruption signs made it possible for residents to evacuate beforehand.
… Why have people continued to live in an area where eruptions occur?
There are many springs at the foot of Mt. Usu. Archaeological research has clarified that people have been living here for approximately 10,000 years. The plateaus of volcanic ash around Lake Toya have been used for sunny agricultural fields and orchards.
Toyako Onsen, a town that was developed after the 1910 eruption, is one of Hokkaido’s most popular hot spring resorts, attracting 700,000 people each year. All of these are blessings of the volcano.
Ocean life is also related to the volcano. A landslide at Mt. Usu approximately 10,000 years ago reached the sea, forming a complex coastline. Crevices between rocks provide habitats for shellfish, crabs, octopuses and other marine creatures. These too are volcanic blessings.
People live here because they’ve benefitted from these volcanic blessings.
People in this area will have to keep thinking about how they can live with the volcano. To keep living here, they must prepare for eruption disasters. What distinguishes the area are tours that are guided by people who are knowledgeable about volcanoes and who can talk about natural disasters and disaster mitigation. In light of this, the area has earned high acclaim and has been designated as a UNESCO Global Geopark.
Taking in views created by the volcano, eating delicious food that owes to volcanic blessings, soaking in a hot spring and thinking of the earth, our home: These are some ways to enjoy the Toya-Usu UNESCO Global Geopark.
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Why do volcanoes erupt?
Japan has 110 active volcanoes, 20 of which are in Hokkaido. Mt. Usu, which is in the Toya-Usu UNESCO Global Geopark, is known as an active volcano that erupts every 20 to 50 years. Lake Toya was created when a volcanic depression called a caldera formed from volcanic activity and filled with precipitation. The reason the Japanese archipelago has so many volcanoes relates to the activity of plates that cover the earth. An oceanic plate has been sinking beneath a continental plate near the Japanese archipelago, and under this archipelago, water is expelled from the upper part of the oceanic plate. This water helps mantle rock to melt, creating magma. Being less dense than the surrounding rock, the magma rises through the ground from buoyancy. The rising magma has created magma chambers under the Japanese archipelago.
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On August 7, 1977, Mt. Usu erupted, spewing out large amounts of volcanic ash and pumice stones to a height of 12,000 m. Such an eruption is called a Plinian eruption. It’s thought that water, carbon dioxide and other volcanic gas components in an underground magma chamber started to foam as a result of some process and that this caused the eruption. Shake a carbonated drink and open the bottle. The pressure release will cause the drink to foam up and spray out. In the same way, volcanic eruptions are caused by the foaming of magma. Look at a pumice stone and you’ll see it has lots of small holes. These are evidence of foaming magma. Most of the eruptions of Mt. Usu in 2000 were phreatic eruptions, in which magmatic substances aren’t expelled. Magma that had risen from underground heated the groundwater above the magma, creating high-pressure steam that caused the eruption. Heat water in a kettle to a high temperature, and the boiling water will sometimes gush out. In the 2000 eruptions, volcanic rocks rained down on houses and roads—rocks that had formed the ground surface.
On your visit to this volcanic geopark, don’t just look out at the view. Look down at the rocks under your feet. Look at a pumice stone and imagine the foaming magma it came from. Feel the volcanic activity!
- The eruption mechanisms outlined in this column are just a few of many examples. Many other volcanoes have different mechanisms.
Toya-Usu UNESCO Global Geopark (by Nire Kagaya, a member of the Toya-Usu UNESCO Global Geopark Promotion Council, and Hikaru Yokoyama, an associate professor at Hokusho University) and Why do volcanoes erupt? (by Hikaru Yokoyama, an associate professor at Hokusho University) are excerpted from a pictorial record book of the second special exhibition at the Hokkaido Museum Let’s Go to a Geopark! They have been modified with the authors’ permission. Around Mount Usu, some buildings were practically collapsed by past eruptions. These buildings still stand as monument, reminding visitors of the past events in the area and providing lifelong learning opportunities to mitigate damages from such natural disasters. For these buildings, conservation efforts are kept minimum. Grasses left grow around the remains recall people to a sustainable relationship between people and wild nature. This also gives them a visible instruction for the course of vegetation recovery over time.

Toya-Usu UNESCO Global Geopark Council
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