Like many posts on volcanoes in remote parts of the world, the direction of this pair changed a bit during research and writing.  My initial interest was in the Hitokappu volcanic group (Bogatyr Ridge with Stokap as its highest point) on Iturup Island in the southern Kuril Islands.  Sadly, there wasn’t a lot of material published about the group.  On the other hand, it is located on a wonderfully volcanic island, Iturup, the largest in the southern Kurils.  Iturup has multiple volcanic systems, calderas, recently active volcanoes, and several active hydrothermal systems.  So, we expanded the scope of the post to survey volcanoes on the entire island. 

Iturup (Etorofu) Island is one of the largest of the Kurils, 200 km long by 7 – 27 km wide.  It is rugged, completely volcanic, with 12 – 20 volcanic systems along its length.  The Japanese list 13, which is what we will review.  Nine of them are considered active.  The highest point is the previously mentioned Stokap at 1,640 m.  There are vigorous hydrothermal systems island-wide.  Given the hydrothermal systems, there was geothermal exploration and multiple wells drilled over the last several decades.  I have not found, an operational geothermal generation station as yet. 

The 3,140 km2 island hosts a population of 7,500.  The island is sparsely populated, with less than 5,000 within 100 km from the volcanoes in the central part of the island. 

Climate here is considered to be temperate marine with wet, cool summers and mild, though snowy winters.  Average summer temperatures reach 14° C.  Feb is the coldest winter month, averaging -3° C.  Frequent snowfalls alternate with thawing throughout the winter.  Rainfall on Iturup is abundant, supporting multiple rivers, streams and waterfalls.  The highest waterfall in Russia is found on Iturup. 

Most of the island is heavily forested with firs, larch and a few broadleaf species.  There are also well-developed bamboo stands that make slopes almost impassable.  Most of the residents live in the only town, KIurilsk.  There are multiple smaller rural villages.  The most significant of what little economic activity takes place on Iturup is fishing, primarily roe stripping salmon.  There is a small mining activity for rhenium deposited by hydrothermal activity on Kudryavy volcano.  The island is reasonably popular for wilderness expeditions staged out of neighboring Sakhalin Island (20 hours away by ferry).  Air service into Kurilsk is also available. 

Visitors are limited to existing roads unless they have specific permission from the Russian government.  While the volcanoes are not particularly tall, the flanks are typically soft, highly eroded, and all but impassable.  Still, there are a few tourist spots of interest.  Infrastructure for traveling and exploring is limited.  The easiest way to explore is via guided tour.  Brown bears are also a danger, especially on the N part of the island.   

Itutup was first inhabited by the Ainu who have been here since the 14^th Century.  Its name is derived from “etorop” in Ainu, meaning jellyfish.  Japanese and European explorers first reached the islands in the 17^th Century.  The island is most infamous for being the staging port for the Japanese carrier fleet that carried out the Pearl Harbor attack Dec 7, 1941.  Soviets and Russian military based air defense fighters on the island since 1945. 

Ownership of Iturup Island has alternated over the years, with Russia claiming ownership in the waning stages of WWII.  This has led to multiple Japanese and Russian names of the island itself and its volcanoes.  The Japanese are still not entirely happy with the loss of these islands, referring to them as the Northern Territories.  Ownership continues to be a sore point between the two nations. 

Volcanoes here are monitored by both Japanese (Japan Meteorological Agency – JMA) and Russian (Sakhalin Volcanic Eruption Response Team – SVERT) scientists.  Both SVERT and its counterpart monitoring volcanoes on the Kamchatka Peninsula work with the Alaska Volcano Observatory (AVO) to provide warnings for regional air travel. 

Region – Iturup (Etorofu) Island

We will limit our regional discussion of volcanoes to those on and near Iturup Island.  Distances are measured from the highest point on the island, Stokap volcano on the S end of the Hitokappi volcanic group.  As this part of the world is volcanically intensive, we have written multiple posts on volcanoes in Hokkaido, the Kurils and Kamchatka over the years.  Until now, haven’t done much in the southern Kurils until now.  The closest we got to them was a Mar 2024 post Hokkaido 6 – Volcanoes of the Shiretoko Peninsula. 

Granyia did an extensive 2017 post on Kudryaviy that is an excellent introduction to Iturup and Medvezhia volcanic complex. 

There are multiple volcanic features of interest to visitors on Iturup.  The first of these is the Yankito Lava Plateau, a lava field stretching from Chirip volcano N of Kurilsk to the Sea of Okhotsk.  Early Neolithic sites around 9 ka are found on the plateau.  It is located some 5 km from the airport at Kurilsk. 

Farther E, still on the Sea of Okhotsk side, we have the White Cliffs, heavily eroded ignimbrite from the caldera-forming eruption(s) creating the Vetrovoy (windy) Isthmus.  These stretch along the sea for nearly 30 km.  Most of the beaches are grey with eroded pyroclastics.  Due to the large number of lava flows into the sea, much of the shoreline is impassable, though picturesque.  Iturup shorelines have been described as similar to those in Iceland, though much less well known. 

Warm mineral baths are a popular activity among residents in this part of the world.  The problem with Iturup Island is that the mineral, chlorine, acidity and most importantly, the temperature of springs and pools varies from spring to spring.  They also vary over time, especially during time of heightened activity.  One web site lists radon springs.  Prospective bathers are warned to be very careful, use a guide, consult healthcare providers, and pay close attention to locations that are (usually) safe before getting into the waters.  Healing waters may be anything but.  Some villages are near thermal waters (baths) that visitors can pay the village for permission to swim in.  These springs and pools are found all over the island.  The most popular are thermal springs at the foot of Baransky volcano. 

Kamui Dake (Rakkibetsudake / Kamyu / Demon)

Demon is located on the extreme N tip of Iturup, 139 km NE of Stokap.  It is a 1,205 km high stratovolcano with a 1.5 km summit crater breached to the NE.  The Ilya Muromets waterfall, one of the highest in Russia at 140 m, falls from the E slope of the volcano into the Pacific Ocean.  Demon is a post-caldera volcano, growing over the last 10 ka, within a glacial valley 3 km E of the highly eroded Kamui volcano.  It is the most recent manifestation of activity at Kamyu.  It is currently dormant.  JMA lists the system as a two-volcano system, Kamui Dake and Rakkibetsu Dake (Demon). 

The Kamyu caldera was explosively formed at the top of an older shield 10 x 18 km in diameter.  The only visible remaining part of the ancestral shield is a scarp along the E and NE side of the caldera.  The caldera was formed pre-glacial.  During the previous intraglacial (100 ka), several pyroclastic cones erupted in the caldera.  The highest of these (Kamyu) was still active when the most recent ice age set in.  Over the last 10 ka, lavas filled a trough created by the last glaciation.  The new Demon cone formed in the trough and was destroyed in a directed blast eruption. 

Moyoro Dake (Moyorodake / Kudriavy / Medvezhia)

Moyorodake is located at the NE end of Iturup Island, 130 km NE from Stokap.  The current edifice tops out at 1,124 m and erupts andesites, basaltic andesites, basalts, dacites and rhyolites.  The Medvezhy caldera has an extensive and violent history, with two overlapping calderas, 14 x 18 km and 10 x 12 km.  VOGRIPA lists the most recent caldera forming eruption as a VEI 7.0, 410 ka that ejected 90 km3 of dacite.

Post caldera activity extruded rhyolite domes in the caldera followed by the Medvezhy dacite cone and subsequent pyroclastics.  Andesite Serdeni cone then formed just W of Medvezhy followed by eruptions of the Kudryavy basaltic andesitic flows farther W.  Fresh basalt flows (undated) surround the small composite cone of Menshoi Brat. There is also a small lake on the caldera floor.  The fourth of these is Moyorodake, which along with Tukap were historically active.  They both have active hydrothermal systems and fumaroles. 

The four small, closely spaced stratovolcanoes are built along an E-W line on the E side of the complex.  The farthest E of these (and highest) is Medvezhy, outside the W caldera, along the Pacific coast.  The rest of these are Moyorodake, Kudriavy (Kudryavyi / Io-dake), Meenshoi Brat (Menshoi Brat / Yake-yama), Srednii, and Tukap. 

There is no significant changes in the chemistry of erupted magma before and after the most recent caldera formation.  Chemistry of the erupted magma is consistent with mantle melts.  Most of the caldera rims have been destroyed by erosion, though there are some wall segments up to 300 m high.  The ancestral volcano is thought to be a shield.  Post-caldera domes erupted large amounts of lavas. 

Kudryavy rises 800 m above the caldera floor and is covered by fresh lava flows.  There is no vegetation on the cone.  There are numerous fumaroles at the top of the cone in the 300 x 70 m crater.  Vent temperatures increase SW – NE, with the highest temperature vents having the strongest discharge.  These fumaroles glow red even during the day. 

Like the rest of the system, Kudryavy erupted basalts to andesites.  The last eruption took place in 1883.  There is a report of a phreatic eruption in 1956, but eruptive products are missing at the summit.  Current activity is quiet degassing from the crater area and one hot spring at the foot of neighboring Menshoi Brat basaltic cone.  This volcano is of particular interest due to high temperatures (up to 940° C) and high gas flow rates from the fumaroles.  There is active deposition of rhenium sulfide, a rare earth element that is mined. 

Although high temperature fumaroles are relatively common at other volcanoes (Merapi, Mt St Helens, Augustine), they are all coupled with extrusive dome growth, the process of an eruption.  Kudryavy is different, and similar to that of Momotombo, Satsuma Iwojima, where it appears the fumaroles are the result of a shallow magmatic system not currently erupting.  High temperatures suggest the presence of magma very near the surface.  This magma is replenished with new batches of volatile rich fresh magma.  Calcium sulphate deposits up to 5 m thick have been found in the rhenium enriched fumarole field. 

The last magmatic eruption from Kudryavy was 1883 erupting a small lava flow.  There are multiple papers published about Kudryavy.  The most recent phreatic eruption was 1999.  This created a new small crater with a vigorous fumarole at its bottom.  The fumarole is 50 m deep with a temperature of over 800° C.  Activity at Kudryavy changed after 1999 with an increase in gas emissions and temperature increases of over 200° C at some of the high temperature fumaroles.  Surface crust of rhenium sulfide disappeared in the “Rhenium Field. 

Menshii Brat volcano is located at the SW end of a post-caldera ridge of volcanoes.  It stands out from the rest of the post-caldera volcanoes.  It is an isolated andesitic to dacitic dome topped with a pair of what are described as slag cones (Korotyshka and Vostok).  The cones erupted basaltic to basaltic andesitic tephras and lava flows.  There is no exact dating of its eruptions as yet, but they appear to be no more than a few hundred years old.  Erupted lavas are among the most primitive magmas erupted in the Kurils and are up to 5% by weight water.  There are outcrops of rhyolitic pumice tuffs at the W foot of the volcano that erupted during caldera formation. 

Volcanic gasses collected from the summit crater of Kudryavy show a mixing between magmatic fluids and meteoric water, with water vapor chemistry emitted similar to altered sea water.  Other trace elements may be caused by magma – marine sediment interaction. 

Groundwaters discharge on the floor of the caldera, creating multiple small lakes.  There is only one known thermal spring, with neutral pH, discharging 39° C water at the base of lava flows from the Menshoi Brat cone. 

Shibetoro (Tsirk)

The 6 km diameter Tsirk caldera is older than 10 ka.  It is located some 115 km NE from Stokap.  There is no information on what it erupts, though given its neighbors, some combination of basalts, basaltic andesites, andesites and dacites would not be a bad guess.  Little is known about this 853 m system. 

While the caldera is visible in relief, pyroclastic deposits from it are not well preserved.  It cuts previous volcanic structures and is overlapped by more recent small pyroclastic cones.  It is possible that the caldera was formed at the end of the last glaciation or during an interglacial.  There are traces of an older glaciation on the inner caldera walls.  The ancestral volcano was a shield that may be as old as 2 Ma. 

Vetrovi (Vetrovoy / Rucharu / Goylets – Tornyi Group) Isthmus

The Vetrovoy (windy) Isthmus divides the N Iturup highlands from the rest of the island.  The isthmus is a 12 km wide tectonic depression bounded by a pair of faults.  There is a chain of dacite domes along the Pacific shore that were extruded close to the time of the caldera-forming eruption.  Post caldera structures include a 200 m high scoria cone in the W part of the caldera, the 0.7 km wide Taynoe (Tayny / Tornyi) Lake maar, and the 164 m high Clumba andesite – basaltic andesite stratovolcano in the N part of the isthmus.

The isthmus was initially considered to have formed by a voluminous eruption that started as submarine explosions.  The exact location of the eruptive center is still debated.  Russian geologic maps outline the source caldera.  There is a larger caldera at the bottom of Prostor Bay which may be an alternate center of explosivity.  Volume of erupted pyroclastics is estimated at 100 km3, putting them among the largest and most voluminous eruptions in Kamchatka – Kurile volcanic belt.  Similar sized eruptions were Uzon (39 ka, 150 km3), Kuril Lake (7-6 ka, 140 – 170 km3), and Gorely (360 ka, 120 km3). 

Pyroclastic deposits fill the depression of the isthmus.  They are up to 264 m thick without any paleosol layers.  The tuffs have been dated 38.5 – 5.4 ka.  They are covered by shallow marine sediments in the E part of the isthmus.  Pumices date around 20 ka, which would tend to confirm the caldera forming eruption(s) took place near glacial maximum when sea levels were at their lowest.  Underlying pyroclastic rocks date around 43 ka. 

An offshore eruption at the height of the last glaciation may have been above sea level depending on its distance offshore, while one during an interglacial would be submarine.  Eruptive products would tell whether this was a wet or a dry eruption.  As far as I can tell, that work has not yet been done. 

The caldera-forming eruption sealed a shallow strait between the Medvezhiy Peninsula to the N and Grozny Ridge to the S.  The eruption sequence was either a single massive eruption or a series of very closely spaced catastrophic eruptions of dacite pyroclastic flows, surges and ashfalls.  The center of the eruption is not visible, though the caldera outlines are visible via aerial photographs.  The caldera is open to the SE.  It joins a N-S fault on the NW and is partly buried by pumice.  There are thick pumice deposits in the region likely from the formation of the Tornyi Lake maar. 

Rucharu includes the small cones Golets and Tornyi.  It is located SW of Moyorodake, 85 km NE from Stokap, along the narrowest part of Iturup Island.  The highest point, Rucharuyama tops out at 437 m. 

The post-caldera cones are undated, but thought to be perhaps 10 k.  Tornyi has a small lava flow in a glacial cut.  The andesitic – dacitie Golets cone is built on the eroded remains of the Parusnaya Mountain volcano.  Its lava flows reached the nearby coast.  These cones and the Parusnaya Mountain volcano are located on the NE side of the 6 – 7 km Vetrovoi Isthmus (Ruchuru) Caldera.  There is a 1 km wide explosion crater with the small Klumba cone on its W margin. 

Chirippu Yama (Chirippusan / Chirip)

Chirip is a 1,587 m stratovolcano on a peninsula jutting NW into the Sea of Okhotsk from central Iturusk, 71 km NE from Stokap.  It erupts basalts, andesites, basaltic andesites and dacites.  The system is constructed of overlapping stratovolcanoes, Kitachirippusan (N) and Minamichirippu (Bogdan Khmelnitskii).  Both of these are constructed on a pre-glacial volcano rising above a 1,100 m saddle. 

Lava flows are truncated by a 4 m wide depression on the W side of the peninsula.  Recent basalts cover older basaltic andesites and andesites.  Kitachirippusan has a shallow summit crater partly filled by a small lake.  Lava flows are found on all sides of the main cone from the summit.  Satellite cones are located on the N flank.  Minamichirippusan lava flows reach the coast on both sides.  There are only two known historic eruptions, 1843 (VEI 2) and 1860 (VEI 1).  The 1860 eruption took place at a vent SE of the Minamichirippusan summit. 

The depression cuts pre-glacial and post-glacial structures and is in turn divided into two parts.  What formed the depression is so far unclear, being either formed by local tectonics or earlier volcanic activity.  There is a thick layer of welded tuff exposed in the N part of the depression. 

Additional information

Volcanoes of Japan, JMA

Active volcanoes of the Kurile islands:  A reference guide for aviation users, USGS Open-File Report 2008- 1162

Petrology of Bogdan Khmelnitskiy volcano (Iturup Island, the Kurils):  a model of fractionation and mixing in the magma chamber, Larin, et al, 1997

National catalogue of the active volcanoes in Japan (the fourth edition, English version), JMA

Geology of the calderas of Kamchatka and Kurile Islands with comparison to caldera of Japan and the Aleutians, Alaska, E Erlich, Open File Report 86-291, USGS, 1986

Geochemisty of magmatic gasses from Kudravavy volcano, Iturup, Kuril Islands, Turan,. Et al, Jan 1997

Volatile trace-element transport in high-temperature gases from Kudriavy volcano (Iturup Islands, Russia), Wahrenberger, et al, 2007

High temperature volcanic gas geochemistry (major and minor elements) at Kudryavy volcano, Africano, et al, Jan 2003

Decade-long study of degassing at Kudriavy volcano, Iturup, Kurile Islands (1990 – 1999):  gas temperature and composition variations, and occurrence of 1999 phreatic eruption, Korzhinsky, et al, Sept 2001

Hydrocarbons in magmatic fluid in phenocrysts of eruption products of Men’shii Brat volcano (Itirup Island): data from pyrolysis-free gas chromatograpy – mass spectrometry of a melt a …, Nizametdinov, et al, Mar 2022

The 2017 activity of the Kurile Islands volcanoes, Rybin, et al, 2018

Gas emissions from volcanoes of the Kuril Island arc (NW Pacific):  geochemistry and fluxes, Taran, et al, 2018

Vetrovoy isthmus of Iturup Island – Holocene strait, Afans’ev, et al, 2019

Water in parental basaltic magmas of the Menshiy Brat volcano (Itutup Island, Kurile Islands), Nizametdinov, et al, Jul 2019

Holocene climatic changes and environmental history of Iturup Island, Kurile Islands, northwest Pacific, Razjigaeva, et al, Jul 2000

Basaltic volcanism of Medvezhia caldera on the Iturup Island of Kurile Isles:  impact of regional tectonics on subduction magmatism, Martynov, et al, Feb 2022

Age, source and distribution of Holocene tephra in the southern Kurile Islands:  evaluation of Holocene eruptive activities in the southern Kurile arc, Razjigaeva & Matsumoto, Sept 2015

The structure of the volcanic lake in the Urbich caldera (Iturup Island, the Kuril Islands), DN Kozlov, 2021

Parental melts and magma storage of a large-volume dacite eruption at Vetrovoy isthmus (Iturup Island, southern Kuril Islands):  insights into the genesis of subduction-zone dacites, Smirnov, et al, Aug 2019

Felsic magmas of the caldera-forming eruptions on the Iturup Island:  the first results of studies of melt inclusions in phenocrysts from pumices of the Lvinaya Past and Vetrovoy Isthmus calderas, Smirnov, et al, Jan 2017

Specific structure of the vegetation cover of the Starozavodoskoe solfataric field (Baransky volcano, Iturup Island) in terms of the development of hydrothermal resources, Romanyuk & Kordyukov, 2020

PGE in the modern hydrotherms of Kudryavy volcano (Kuril Islands), Distler, et al

Modern postvolcanic activity of Beratarube volcano, Iturup Isl., the Kuril Islands, Degterev, et al, 2020

Ultra acid sulfate chloride waters of Baransky volcano on Iturup Island, Kurils.  The composition and output of magmatic and rock-forming components, Kalacheva, et al, Oct 2022

Hydrogeochemistry of thermal waters of Baransky volcano, Iturup Island (Southern Kurils), Bragin, et al, Jul 2015