Introducing Volcano Mount Tsurumi and the Beppu hell springs

[BrickFielder]

Introduction
My intention is to produce a series of articles (depending on interest) which introduces ideas about volcanic and earthquake activity. I want to go slightly off the beaten track to explore oddities, volcano hazards, analysis methods, Wonders and Mankind’s impacts. Keep in mind I am not expert (corrections gratefully received), but hopefully these will at least give a flavour of some different places in the world and provide a few minutes escape from people’s troubles.

Introducing Volcano Mount Tsurumi and the Beppu hell springs

Reason for Interest
Some places are just unique and Beppu City falls into that category. A city with over 3000 hot springs that shrouds the city in hot mist in the early morning is an unusual sight. Bearing in mind that Mount Tsurumi Magma provides heating for the springs and lives in the same tectonic setting as Mount Aso this seems a risky place to find a city. Perhaps surprisingly the greatest risk here is from Tsunamis or landslides caused by earthquakes.

Beppu hell springs
The Japanese town of Beppu on the island of Kyushu is perpetually shrouded in steam thanks to almost 3,000 of hot spring vents that eject over 130,000 tons of scalding water on a daily basis. Only Yellowstone National Park in the US discharges more. Dubbed the Hells of Beppu due to the high temperatures they record, the hot springs remain relatively unknown outside of Japan. The hot springs in Beppu record high temperatures of water with some said to reach the boiling point of water. Some of the springs(hells) have become tourist attractions with the number of visitors frequenting the area can rise up to 60,000 people. Beppu Park is also popular at the center of beppu with flower gardens and hanami trees in cherry blossom at the right time of the year.

Umi Jigoku or the Sea Hell is a beautiful cobalt blue color. The temperature of the pond is so hot that it stays at a rolling boil and can poach an egg. It has a large mass of bubbling aqua blue water, secondary orange coloured hells, lotus flower pond, foot onsen (bath).

Oniishibou Jigoku or Shaven Head Hell, is a mud pool. The boiling temperatures of the water make mud bubbles at the surface. The pond is named for the resemblance of the mud bubbles to the hairless head of a Buddhist monk.

Yama Jigoku or Mountain Hell was formed by a mud volcano that also made a small mountain with small ponds around it.

Kamada Jigoku or Cooking Pot Hell is a group of several bowling springs. A statue of the devil is perceived to be the chef. As these ponds are cooler than the other springs, tourists can drink the water and enjoy snacks cooked in the pond.

Oniyama Jigoku. The pond is known by Crocodile Hell as it is home to 100 crocodiles. The pond is also known as Demon Mountain Hell as the spring generates a lot of steam. The steam is said to be able to generate enough power to tug one and a half train cars!

Shiraike Jigoku or White Pond Hell, is named for the white steam coming off the pond and blanketing the area. The waters are a milky white tinged with emerald from the sassolite minerals.

Tatsumaki Jigoku or Spouting Hell, features a geyser that spouts every 30 minutes for about 10 minutes. The water can reach a height of 160 feet.

hinoike Jigoku or Blood Pond Hell, is named for the distinctive red water of the pond from the water's high iron content. The water has antiseptic properties, and tourists can dip their toes downstream or purchase a mud paste.

Kinryu Jigoku or Golden Dragon Hell is named for a dragon statue at the pond that looks as though it has come to life from steam rising from the pond coming out of it's nostrils. The rim of the pond also has a golden sheen.

The Keicho Bungo earthquake

During 1596 an earthquake with strength m7.3 occurred out in the Bay of Beppu. A recent high resolution shallow water profiling survey revealed recent activity of submarine fault which was newly found to fill a gap between two subaerial faults, the Asamigawa and the Funai faults running on the southern coast of Beppu Bay. Historical records suggest that this activity on the north-dipping normal fault corresponds to Keicho-Bungo earthquake. Core samples obtained from the both sides of the newly found submarine fault suggest repeated occurrence of this simultaneous rupturing with recurrence being approximately 460–1850 years. Records and modelling suggest that the tsunami height was over 8m and travelled many kilometers inland at low lying areas. In addition there were reports of the earthquake triggering landslides which created more tsunamis and damaged farms on the volcano.

The Tectonic environment
The Japanese archipelago consists of four main islands aligned north to south and surrounded by smaller islands. Kyushu is the southernmost of the four islands.

It is located on the Eurasian Plate which is bordered to the southeast by the Philippine Sea Plate.  Generally in Japan magma is believed to form when the Philippine Sea Plate is subducted beneath the Eurasian Plate. Unlike the rest of Japan, Kyushu is situated  in an extensional region and for that reason a rift has developed running from east to west across the island. The Beppu Shimabara graben (rift) extends NE SW of the center of Kyushu Island with the Beppu geothermal field being situated within 30 km on the eastern flanks of Mount Garan and Mount Tsurumi. Earthquakes that have occurred in this graben shows that the cut off depth of the earthquakes increases with the distance from the Mount Tsurumi volcano, which is considered to reflect the temperature structure affected by a high-temperature magma body under the volcano. The earthquakes are probably triggered by the fluids migrated from the magma body into the brittle crust under active stretching. There is an active seismic cluster in the eastern flank of the volcano near the southern border fault of this graben which is an area of localized increases subsidence.

The Volcano
This volcano group consists of lava domes stretching 5 km north-south across the Beppu graben, which itself extends from east to west behind Beppu city. Tsurumi is at its southernmost end. The volcanoes in the group are composed of andesite and dacite (is between 57 and 63 wt %). Tsurumi is composed of deep lava flow deposits. A weak fumarole is located on the northern side of the summit of Tsurum, and very active fumaroles are in the crater of Garan, at the northern end of the volcano group. The alluvial fan at the east foot of the volcano group contains the Beppu Onsen group, and a particularly large number of boiling springs and fumaroles are distributed on the border between the fan-shaped north-south rim and the mountain land. On the northern side of the summit of mount tsurui are fumaroles and there is strong fumarole activity on mount garan.

Beppu Ropeway goes up Mount Tsurumi, with an altitude of 1,375m and is Kyushu's largest ropeway. It has a capacity of 101 passengers, and it only takes about 10 minutes to reach the top. Rising above Mount Tsurumi you can enjoy the cherry blossoms in spring, the Miyama Kirishima flowers that are only seen in the high mountains of Kyushu, the silver frost spreading across the land in winter, and the autumn colours in autumn.

Past Eruptions
 There was a 200 AD eruption was large (VEI=4), explosive, and generated pyroclastic flows. During 771 and 867 there was Tephra fall and a Lahar from Garandake. The Garan eruption resulted in lots of fish deaths in the local rivers.

Recent Activity
In 1949 Many white fumes approximately 10 m high and with temperatures of 95 °C  were detected in an oval-shaped area at an elevation of 1100 m, approximately 500 m northwest of the summit of Tsurumi.
In 1974 Fumes more fumes detected at the same location as 1949 but rising to over 100m High.
In 1995 A mud volcano was formed at a former silica excavation site on Garan. The oval mud volcano grew until it was approximately 10m across and 4m deep.
In 1999 was an increase in earthquakes with hypocenter approximately 3km east of the summit of Tsurumi, with a depth of roughly 5 km.
Since the 2011 off the Pacific coast of Tohoku Earthquake earthquake activity has increased between roughly 4 and 5 km
below the western and eastern sides of the summit of Tsurumi.

Discussion
Realistically the volcanic or earthquake risks here are pretty low, but to call it dormant would also be a stretch. I guess it is just so complex and unusual that it warrants more attention.