Introducing the highlights (16 geosites) of the South Izu area

The highlights of the South Izu area
Ryugu Sea Cave & Sand Ski
The skylight of Ryugu cave is one of the largest in Izu, and you can stand under the skylight through the cave from the entrance.
The ceiling of a large sea cave collapsed, and a skylight about 50 meters in diameter opened. The walls of the cave are beautifully layered with tan tuff erupted from a submarine volcano, and the contrast with the blue seawater that fills the bottom of the skylight is mysterious.
On the northern shore of Ryugu Cave, there is a sand bank made of piled sand blown by strong winds. The blown-up sand maintains a 30-degree tilt angle and people play sled on the natural slide.
On the surrounding cliffs, you can see volcanic ash and lava flows that erupted into the sea and cracked, and traces of magma intruded through them.
Ebisu island is a small island that can be crossed by a bridge. The promenade that circles the island retains the remnants of ancient submarine volcanoes, such as the beautiful stripes created by pumice and volcanic ash, and the rough submarine debris flows.
The stratum slightly tilted by crustal deformation changes one after another along the promenade. Standing on the south side of the island, you can overlook the wave cut terrace called “Senjojiki”, Izu Islands and Mikomoto island.
Iruma Senjojiki
Senjojiki of Iruma, a 40-minute walk from the port of Iruma, which can be said to be a secret area of Izu, has a beautiful stratum made of volcanic ash and pumice that has accumulated on the sea floor.
On the cliff of Cape Mitsuishi, which rises in front of Senjojiki, magma that has risen from the underground has intruded the stratum of white volcanic ash.
Tawaraiso & Takanba
On the west side of Tsumekizaki, the scenery of piles of columnar rocks called "Tawaraiso" is spreading all over. This is called a columnar joint, and when the magma cools and hardens, its volume shrinks and cracks occur.
These columnar joints are formed inside rocks called “sills” formed by magma entering along the surface of the stratum that has accumulated due to the eruption of a submarine volcano, and appear on the surface due to uplift and erosion.
The coast of Takanba, where traces of submarine volcanoes remain, is reddish due to underground hydrothermal activity, and various minerals such as zeolite are generated in rock cracks (cannot be collected).
You can also observe the step-like terrain (sea terrace), which is a flat surface that has been eroded by the wave and has been raised due to crustal deformation.
Kawazu Seven Waterfalls
Approximately 25,000 years ago, the lava effused from Noborio-minami volcano flowed into the valley. Columnar joints are formed inside when the lava flows fill the valley and cool down. Subsequent erosion of the water stream resulted in columnar joints appearing along the stream, creating as many as seven waterfalls in a valley spanning one kilometer.
From the upstream, Kamadaru, Shrimp Falls, Snake Falls, Shokeidaru, Crab Falls, Deaidaru and Ohdaru continue. Upstream of Kamadaru, there is a deep pool called Sarutabuchi.      
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Yusuge Park
Many of the coastlines around Irozaki are made of volcanic ash and lava erupted from submarine volcanoes, resulting in rugged terrain due to years of wave erosion.
There is Yuusuge Park, where gentle hills spread and Yuusuge (daily lily) grows naturally.
This gentle hill was created by reclaiming the steep valley with the lava of Nanzaki volcano that erupted about 400,000 years ago.
Shimoda city
As you walk down the streets of Shimoda, you will see the plaster wall called "Namako Wall" and the "Izu Stone" wall. Izu stone used in warehouse is cut out of volcanic ash and pumice tuff erupted from a submarine volcano.
In the vicinity of Perry Road in Shimoda, buildings using Izu stone are used for stylish stores.
Yumigahama & Ounohama Beach
Yumigahama appears on the coast of Minamiizu, where steep cliffs continue. The white sand beach, which draws a beautiful arc of 1200 meters, was created by the sand particles flowing down the Aono River. The sand particles that flowed into the sea were swept away by the current and accumulated in a strip extending from southwest to northeast. The long and narrow cape is called a sand spit. The plain behind the sand spit was once a cove.
To the east of Yumigahama, where the white sand beach is beautiful, is Ounohama beach, where the rocks spread. Submarine volcanic products created a unique landscape, including radial fissures formed in magmas that intruded the stratum such as debris flows that flow down the sea floor. There are strangely shaped rocks called sparrow rocks and shrimp holes.
Irozaki Cape
The rocks that spread around Irozaki, located at the southernmost tip of the Izu Peninsula, are lava flows that erupted on the sea floor. When the lava erupts into the water, it is rapidly cooled by the water and becomes a set of shattered rock fragments.
The cliff of Irozaki has many hollows like a beehive, and the Iro Shrine is made using these hollows.
Kakizaki Bentenjima
Kakizaki Bentenjima has a distinctive stratum with beautiful striped patterns. The striped stratum is formed by ash and pumice erupted from submarine volcanoes millions of years. Bentenjima was uplift by crustal deformation then eroded by the waves.
On this stratum, cross-lamination and fossil traces can be observed. v
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Under the volcano, there is a magma path through which magma passes from deep underground. The path of this magma that emerges on the earth's surface due to crustal deformation is called "volcanic neck".
At Nakagi Port, the powerful scenery of columnar joints which growed inside the volcanic neck spreads. Columnar joints are created by shrinking as the magma cools and hardens.
Sirahama Beach
The white cliffs surrounding the Shirahama Beach are stratun of volcanic ash and pumice that have accumulated on the seabed during the submarine volcanic era before Izu became a peninsula.
It is one of the best beaches in Japan with white sandy beaches and emerald green seas, and is also a surfing mecca. A part of the rocky shore is also a sanctuary of Shirahama Shrine.
Hachinoyama Volcano
Mount Hachinoyama is a pudding-like scoria cone created by an eruption about 36,000 years ago and is one of the eastern Izu volcanoes.
At the cuts and promenades near the summit, the scoria piled up forming a beautiful stratum.
On the top of the mountain, you can see a group of stone Buddhas enshrined in 1737.
Saganogawa Valley
Some of the lava that flowed out of Mt. Hachinoyama during an eruption about 36,000 years ago is flowing down along the current Sagano River.
A promenade is maintained along the Sagano River. Along this promenade, the Sagano River flowing over the lava flowing down from Mt. Hachinoyama and the columnar joints formed when the lava cools down create a beautiful scenery.
Looking at the exit from the bay from the port of Mera, you can see a stratum that intruded vertically inside of the striped layers exposed on the high cliff. This is a dike where magma has intruded cracks in the stratum of volcanic ash and debris flow that have accumulated on the sea floor.
The appearance of a giant snake crossing a cliff is called "Jakudari". The pattern that looks like a snake scale is a columnar joints.
In the middle of the Hiyoriyama promenade from Koura Port, a group of stone buddhas called "33 Kannon" is enshrined in a depression of sea cave. The stratum behind "33 Kannon" contains a lot of rocks, which are formed when volcanic products are rapidly cooled, and are formed by submarine volcanic eruptions.