日光白根山 - Nikkō-Shirane - 11/4/2023

About: Mount Nikkō-Shirane (日光白根山, Nikkō-Shirane-san) is a stratovolcano in the Nikkō National Park in central Honshū, the main island of Japan. It stands at 2,578 m high. It is the highest mountain in north eastern Japan (no higher mountains exist in the east or north of this mountain). Its peak (Mt Okushirane) is a Lava dome of andesite. Mt Nikkō-Shirane is listed in the 100 famous mountains in Japan proposed by Kyuya Fukada and also of one of the famous mountains of Tochigi and Gunma prefectures respectively.

It should not be confused with Mount Kusatsu-Shirane elsewhere in Gunma Prefecture. It is located at the boundary between Nikko City, Tochigi Prefecture and Katashina Village, Tone County Gunma Prefecture.

Mt. Nikko Shirane is surrounded by the mountains of the Shirane volcano (Neogene volcano) and is often hidden by clouds throughout the year. From the Kanto Plain only the dome-shaped (Quaternary volcano) summit is visible.

In winter if the weather conditions permit, the white snow fields on the darker surroundings slopes can make the mountain and peak appear exceptionally white.

Its peak is the highest point in both Tochigi and Gunma Prefectures. The area around Shirane Volcano is designated as Nikko National Park in which there are various natural features such as Goshiki pond, Yuno lake, Yu falls, Senjo moor, and Odashiro moor. Being a designated national park, the alpine plants and vegetation are protected.

The plant Sycamore mallow, which naturally appears on this mountain, can hardly be seen at the present time, with the withering of these plants also in the surrounding mountains, which is caused by air pollutants coming from the Tokyo metropolitan area.

"Shirane" means a white mountain covered with snow, hence such name can be found in many places in Japan. In order to distinguish this mountain from other "Shirane", this mountain is called "Nikkō-Shirane". Its name in Japanese is written 白根 (shira-ne) which are the characters for white and root respectively. The peak Okushirane is written 奥白根 (oku-shirane) means deepest, or inner-most. Whilst there are many mountains in Japan with a similar name, in the 1 / 25,000 topographic map "Mt. Nantai" published by the Geospatial Information Authority of Japan, only Mt. Shirane is described. (Source: Wikipedia)

Geological Summary: Nikko-Shiranesan is a relatively small, 2578-m-high andesitic volcano consisting of a group of four lava domes resting on a shield volcano that rises to the NW of scenic Lake Chuzenji in Nikko National Park. All historical eruptions, recorded during the 17th-20th centuries, have consisted of phreatic explosions from Shiranesan, the youngest lava dome. Viscous lava flows with prominent levees from the underlying shield volcano Keizukayama were responsible for the formation of several scenic lakes north of the volcano. (Source: Global Volcanism Program) 

The mountain has been selected by the Volcanic Eruption Prediction Council as a volcano that requires a complete monitoring and observation system for volcanic disaster prevention.

It is a volcano that has a depression due to erosion between Mt. Shirane and Mt. Goshiki, which are composed of old Neogene volcanic rocks around the highest peak, Mt. Okushirane. This is a newly formed lava dome where there are mountains of the Shirane volcano group such as Maeshirane, Goshikiyama, Sotoyama, and Shiranekakuzan, which are stratovolcanoes.

About 5300 years ago, there have been several large-scale eruptions, and it is believed that there are more than four eruptions that left sediments in the vicinity.

Notable Eruptions and Seismic Activity

- 1649 - steam eruption. Pyroclastic fall. Eruption at the summit crater. A new crater with a large amount of ash fall and a diameter of about 200m and a depth of about 10m was formed. The top shrine was completely destroyed.

- 1872 May 14 - steam eruption. An eruption occurred on the flank of the southwest slope, and a crater with a diameter of more than 200m was formed on the flank of the southwest slope.

- 1873 March 12 - steam eruption. Pyroclastic fall. Eruption location unknown.

- 1889 December 4th - steam eruption. Pyroclastic fall. Eruption at the old crater facing Ogawa Village on the western slope of Mt. Shirane.

- 1952 July-September - smoke and ring.

- 1993-95 Various times - Earthquakes and volcanic tremors. Micro-seismic activity near Lake Chuzenji and micro-seismic / tremor activity just under the summit.

- 2001 March 31-early April - Earthquake, seismic activity in the northwest to northeast of Mt. Shirane, Nikko (depth less than 5km).

- 2011 March - Earthquake. After the 2011 Tōhoku earthquake and tsunami, seismicity increased around 5km to the west and northwest, and from 5 to 10km from the east to the southeast. (Source: Wikipedia)