Interesting topography and geology of the Kumano Kodo. Eight recommended geo-sites

The Kumano Kodo is a World Heritage Site. Since the Heian period (794-1185), many people, regardless of status, have walked this pilgrimage route to the ‘Kumano Sanzan’ (three mountains of Kumano). It is known as a power spot and is visited by many tourists from abroad.

In fact, Kumano Kodo is known as a very unusual place geologically. The ‘Earth Park’, where visitors can learn about how the earth is formed, is called a geopark. The nine municipalities of Shirahama Town, Kamitonda Town, Susami Town, Kushimoto Town, Kozagawa Town, Ochi Town, Nachikatsuura Town, Shingu City and Kitayama Village, where Kumano Kodo is located, are magnificent Geoparks where you can experience the history of the earth.

Geology and rocks of the Kumano Kodo

The foundations of the land in Nanki-Kumano, where the Kumano Kodo is located, were laid as far back as 70-20 million years ago. Over the long time since then, the land has been uplifted and bent, the strata have been broken by volcanic activity, magma has flowed into the land… and about 2.6 million years ago, the current topography was formed.

Therefore, in the western part of Kumano, you can observe the strata bending, cracking and shifting, while in the eastern area where volcanic activity occurred, you can observe the geological formations caused by volcanic activity.

Volcanic geological formations include whitish rocks with large mineral crystals, which are formed when magma hardens, and ‘pyroclastic rocks’, which are formed when volcanic ash and other materials harden.

8 spots (geosites) where the geology of the Kumano Kodo can be seen.

Spots where you can enjoy Geoparks are called ‘geosites’. In this article, we introduce eight of the 107 geosites in Kumano that we particularly recommend.

Even those who have never been interested in geology can enjoy these spots. Also, as the spots are located along the Kumano Kodo, you can experience the unusual geology of Kumano while trekking along the Kumano Kodo.

Even those who have visited the Kumano Kodo many times can enjoy the freshness of seeing each place of interest from the perspective of ‘geology’.

The locations registered as Geo-Sites can be found on the official website of the Nanki-Kumano Geopark.

Nachi Waterfall

Kumano Nachi-taisha, one of the three mountains of Kumano. Nachi has many waterfalls, the highest of which is Nachi-no-Taki (Nachi Waterfall). Also known as the ‘First Waterfall’, it boasts the highest drop in Japan at 133 m. The sheer scale of the waterfall is breathtaking. The sheer scale of the falls is breathtaking. It is the symbolic site of the Kumano Nachi-taisha shrine, and even before the Nachi-taisha shrine was built, deities were worshipped around the falls.

Nachi-no-Taki Falls were formed at the boundary between silicon dioxide-rich ‘rhyolite’, which was formed by the rapid cooling of magma, and softer strata. Rhyolite is characterised by its resistance to erosion, and while the softer strata were eroded, the rhyolite was not so much eroded, allowing the waterfall to flow at the boundary.

This is an essential spot for Kumano pilgrims, so feel the sanctity of the place and observe the unusual geological features.

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Gotobiki rock on Mt Kamikura

Gotobiki Rock is a large rock that suddenly appears on a mountain slope. It is named ‘Gotobiki’, which means ‘toad’ in the local dialect, because it looks like a toad. It has a spherical shape that is hard to believe it was formed naturally. Rocks weathered into a spherical shape like the Gotobiki rocks are called ‘core stones’.

Like Nachi Falls, Gotobiki Iwa was formed by the weathering of rhyolite, a type of Kumano acidic igneous rock, and is a 17-minute walk from Kumano Hayatama-taisha Shrine. According to books such as Kumano Gongen Gotobiki Engi, the Kumano gods descended from Gotobiki Iwa on Mount Kamikura, and a palace was built to enshrine them in the present location in the 58th year of the Keiko Era. At that time, the shrine was named ‘Shingu’ in contrast to ‘Motomiya’ on Gotobiki Rock. In other words, it is the place of origin of the Kumano faith.

Gotobiki Rock is clearly visible from the sea, so it was also used as a landmark for ships.

This Kamikura Shrine is home to the famous Oto Matsuri festival. Designated as a national Intangible Folk Cultural Asset, the festival takes place on 6 February every year and involves nearly 2,000 men running down stone steps while carrying torches. The participants are called ‘Agariko’, dressed in white with a rope wrapped around their waists, and many visitors come to see the powerful Agariko run down the steps as soon as the gate opens.

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Giant rock at Shimizu Pass

Shimizu Pass is an ancient road that runs along the border between Kushimoto Town and Nachikatsuura Town. It is located along what is known as the ‘Ohechi’ of the Kumano Kodo routes. When you climb up the slope near the entrance on the Kushimoto Town side, you will come to a rounded vein of rock that looks like the back of a large whale. This is the ‘Giant Rock of Shimizu Pass’.

Shimizu Pass follows the Kozagawa arcuate rock vein, one of the 100 best geological features in Japan. Here you can observe the arc-curved igneous veins.

Monoliths of the Kozagawa River

Giant rock walls can be observed in the Kozagawa River. The monolith of the Kozagawa River, which rises 500 m wide and 100 m high, is a sight to behold. The surface has been eroded by the river and is extremely smooth.

The Kozagawa Arcuate Rock Vein was formed approximately 20 km long between 15 and 14 million years ago. It is thought to have provided a passageway for magma to erupt to the surface. A folk tale of a guardian dog called ‘Ichimaiwa no Mamoruinu’ (The Guardian Dog of Ichimaiwa) has been preserved on this rock face, where the shadow of a giant guardian dog appears every year in April and August.

If you visit Ichimaiwa, you should also observe the pebbles on the banks of the Kozagawa River. Many of the rocks in this area were formed by volcanic activity, so you can see both whitish stones formed by solidified magma and brownish ‘pyroclastic rock’ formed by volcanic ash and other deposits.

Sukumadani.

The Salvation Horse Valley Kannon is the largest Kannon Sacred Temple in the Kinan region. The temple is characterised by its monolithic rock and integrated temple.

The thick sandstone conglomerate layer (basal conglomerate layer) of the Salemadani is resistant to weathering and erosion, which has created cliffs on which the Salemadani Kannon was built. Geological structures known as accretionary bodies, which are formed when oceanic plates are subducted into continental plates, can be seen here.

Mudstone Mountains of Shirahama

The Shirahama Mudstone Veins are designated as a national natural monument. The mud formations that had been deposited earlier liquefied under the weight of the overlying strata and rose several hundred metres into the gaps in the geology above.

As a result, interesting geological formations known as ‘mudstone ranges’ can be observed. Shirahama is known as a valuable place where a number of mudstone ranges can be seen.

Phoenix Fold (Phoenix Cliffs).

Folds are the marks of ancient geological changes. The Phoenix folds are said to be the result of geological changes that occurred between 20 and 40 million years ago, and have been included in foreign geological literature and science textbooks because of their sheer scale.

The folds were formed when sandstone layers were pushed towards land and folded before they had completely solidified, and the folded strata can be observed in the shape of a ‘pentagon’ or ‘cuneiform’.

The area is quite dangerous, so climbing shoes are essential. Guided tours are also organised by the Nanki-Kumano Geopark Centre, so first-time visitors are advised to take advantage of this.

Hashigui-iwa (Bridge Pile Rock)

Hashigakeiwa is a rock tower 15 m wide and 900 m long. The rock was formed approximately 15-14 million years ago when magma rose from underground and penetrated the Kumano Formation.

As the size of the rocks decreases the further away they are from Hashikaiwa, it is thought that the rocks were carried away from Hashikaiwa by the tsunami, and research is being conducted to estimate the size of the tsunami from these rocks.

The site is also home to folk tales of Kobo-Daishi and the Celestial Demon and of the Honest Man and the Sea Monk, and is also a breeding ground for the Uchi Yamasennyu, a very rare bird species, making it a place that can be enjoyed from a non-geological point of view.