Diky (Dikii) Greben is a post-caldera dome complex in southern Kamchatka. The original caldera eruption created the 27 x 18 km Pauzhetka caldera some 443 ka. The most recent caldera eruption created the 7 km diameter Kurile Lake caldera 7.6 ka. Diky Greben and several neighboring stratovolcanoes were constructed following that eruption.
The 1,040 m volcano is located in the Volcanoes of Kamchatka UNESCO World Heritage Property.
The area is sparsely populated with less than 4,600 within 100 km.
Kamchatka generally has a subarctic climate, with cold arctic winds from Siberia combining with moisture laden winds from the cold Oyashio current to provide plenty of snow Oct – May. Weather is generally much wetter and milder than eastern Siberia. The eastern part of the peninsula is rain-drenched and heavily glaciated. The interior valley is much drier. The northern part of the peninsula has a polar climate. Summers can get as warm as 19C, winters as cold as -41C. The volcanoes and glaciers play a role in forming Kamchatka’s climate.
While most tourists visit in the summer, there is a growing winter sports activity.
Diky Greben is monitored by KVERT. It does not appear to have either an active webicorder or webcam.
The region is complex with at least two massive calderas, multiple stratovolcanoes, and the Diky Greben dome complex.
The 27 x 18 km Pauzhetka Caldera is the southernmost tip of the Kamchatka peninsula. It currently has two active volcanoes – Diky Greben and Iliinsky. It also has the Kurile Lake Caldera. It is surrounded by the eroded remains of the Golygin igimbrite, which is the only known product of the caldera forming eruption. The ignimbrite is strongly welded and dates around 448 ka. Total magma volume for this eruption has been estimated at 200 km3, but this estimate was made before airfall and tephras from the eruption had been identified. The dispersal of the airfall and tephras is also unknown. There are only a few later explosive eruptions within the caldera identified. A late Pleistocene proto-Kurile Lake caldera was suggested in the eastern part of the main caldera, but products from this have never been identified.
Ocean cores were sampled from five locations 550 – 670 km from the caldera in 2016. Multiple layers 4-8.5 to 50 cm were identified and chemically matched to the Golygin ignimbrite. There was a range of dates of the tephras 446 – 418 ka. Total erupted volume is now estimated in the range of 330 – 360 km3, making it the second largest documented eruption for Kamchatka, smaller than the 1.78 Ma Karymshina caldera.
Following formation of the Pauzhetka Caldera, post eruption activity built multiple stratovolcanoes surrounding it. To the NW was Zheltovsky. To the SE were Kambalny and Kosheleva. Pre-Iliinsky was constructed in the eastern wall of the Pauzhetka Caldera.
The 8.4 – 7.6 ka Kurile Lake (KO) caldera forming eruption was the largest Holocene eruption in the Kuril – Kamchatka volcanic arc at 140 – 170 km3. The eruptive sequence produced at least three main units: initial phreatoplinian deposits; Plinian fall deposits; extensive ignimbrite sheets, surge beds, and fallout. The fall deposits covered over 3 million km2, mostly to the NW. Ashfall deposits in lakes 6 – 0.1 cm thick were found 1,000 – 1,700 km from the source.
The 76 km2 Kurile Lake is 81 m above sea level. It drains into the Sea of Okhotsk. In the mid-Pleistocene, the region may have been an island, separated from the rest of the Kamchatka Peninsula.
This part of Kamchatka is highly explosive, with 4 of 6 Holocene eruptions with tephra volumes greater than 10 km3 located in southern Kamchatka. The Kurile Lake caldera is 50 km S of the Ksudach Caldera complex, which produced at least 5 caldera forming eruptions.
Recent eruptions from surrounding volcanoes include Zheltovsky in 1923, Illinsky in 1901, Kosheleva and probably Kambalny in the 17th Century.
The entire region rests on older volcanic and sedimentary rocks. More recent volcanism formed lava plateaus, multiple calderas, and stratovolcanoes. The pre-Iliinsky volcano created a somma, which is now filled with the modern Iliinsky.
The KO eruption took place after about a 1,500 period of volcanic quiescence in southern Kamchatka. There are a few tephra layers from distant volcanoes, but only one from the Kurile Lake area, likely due to a small dacite eruption in the depression pre-dating the caldera by 2.5 – 1.5 ka. It is the only known Holocene precursor to the caldera eruption.
The caldera region has been difficult to define. While there may be multiple suspected Kurile Lake calderas, this is more likely to be an artifact of the proximity to pre-Iliinsky which collapsed into the new caldera immediately after caldera formation. The caldera rim cuts the pre-Iliinsky volcano. The lake has two basins divided by a ridge. This was interpreted for a time as a separate Iliinsky Caldera. However, the deposits do not indicate two separate eruption centers. Rather, the depression was formed by a combination of the KO eruption itself and a flank collapse of the pre-Iliinsky edifice. There are multiple younger landslides into the new caldera from Iliinsky and Diky Greben along with alluvial fans. There is a low-density body about 10 km across at a depth of 4 km below the lake.
The KO eruption began with a phreatoplinian phase, likely though a proto-Kurile Lake. Earthquakes associated with this phase likely caused sector collapse and landslides from the pre-Iliinsky and scarps of the old Pauzhetka Caldera. The initial eruption produced rhyolitic ash and a sequence of pyroclastic flows. Initial ash covered over 500 km2. The pyroclastic flows traveled up to 9 km from the vent. This phase likely triggered the catastrophic Plinian eruption.
The eruption changed to a sustained Plinian column. Tephra fell over much of the southern Kamchatka peninsula. Tephra depths close to the vent are over 5 m. As the eruption vent widened, the column collapsed and produced the pyroclastic flows.
The final stage of the eruption produced ignimbrites and cross-bedded surge deposits. Flows traveled up to 50 km from the vent. Magma type transitioned from rhyolite to basaltic andesite and back to rhyolite during the course of the eruption. There is no ignimbrite to the west of the caldera which may indicate an asymmetrical chamber or asymmetrical draining of the chamber. Water was an important component during this phase as the ignimbrites were emplaced over rivers and other wet regions. This eruption was sufficiently powerful to put an ignimbrite flow up and over a 1,000 scarp of the original Pauzhetka Caldera
Eruption of Iliinsky took place soon after the KO eruption. Lava flows and tephras overlie those of the KO eruption. Eruptions from Iliinsky took place between 7.6 – 6.5 ka, producing basaltic andesites, dacite lava flows and tephras. There was a 1.7 ka quiescent period before activity resumed 4.8 ka. This became more intense around 4.0 ka. The cone was built to its current shape by 1.9 ka after which the volcano became quiet once again. It last erupted a phreatic eruption in 1901, creating a large crater on its eastern slope. Tephra from this eruption has been found as far as 100 km from the volcano. This may be the beginning of a new phase of activity for Iliinsky.
Kambalny started forming in the early Holocene. Its edifice was destroyed around 7.2 ka with a series of sector collapses. One of those created the largest Holocene debris avalanche in Kamchatka. Later eruptions built a new cone, almost filling the collapse crater. A large phreatic eruption 650 years ago covered the SW slope of the volcano with tephras. These dispersed as much as 150 km from the volcano. Eruptive products are primarily basalts and basaltic andesites.
Kambalny is the southernmost active volcano of the Kamchatka arc. It is strongly asymmetrical. Lava flows on its older western slope are not overlain by any glacial deposits. Around 6.3 ka, the volcano was destroyed by debris avalanches that formed at least three debris avalanche units. The older two are lava blocks and splintered scoria. They were first mapped as lava flows. The first traveled 14 km SE. After the collapse, a series of strong explosive eruptions built a new cone. These eruptions also covered the first collapse with thick ashfall.
The second collapse involved both old and new cones. The avalanche overtopped 350 m hills and formed a 5 x 20 km deposit SSW from the volcano. The third collapse also involved the landslide amphitheater and some rocks of the older cone. It traveled more than 10 km down a neighboring river valley and is considered to be a wet avalanche. Total volume of all three units is estimated at 5 – 10 km3. He amphitheater now hosts permanent snowpacks and glaciers. Any resumption of volcanic activity will likely trigger lahars and new wet avalanches. The remaining volcano is strongly asymmetric with hydrothermally altered and water-saturated rocks.
Zheltovsky was active 4.0 ka. It entered a long quiet period until 500 years ago when volcanic activity resumed. In the early 1800s, there was a large explosive eruption that produced basaltic bombs, lapilli and lahars which reached the Pacific coast. Eruptive products are basalts and andesites.
Kosheleva produced a large explosive eruption around 7.4 ka. Its tephras were found more than 50 km from the volcano. Later eruptions produced lava flows and a cinder cone on its flank. It has been dormant since 3.0 ka. Kosheleva erupts basalts, andesites and dacites.
All five of these volcanoes produced strong VEI 5 eruptions in the Holocene followed by long periods of repose.
Islands in the Kurile Lake are either post-caldera extrusive domes, submerged pyroclastic domes, or collapsed blocks from the pre-Iliinsky volcano. One of them, Serdtze Alaida is an extrusive dacite dome rising over 300 m from the lake floor. It is chemically similar to the dacites in the KO tephras.
Duration of the eruptions from initial KO subplinian eruptions to formation of Iliinsky and Diky Greben may have been only a few decades. This was the strongest pulse of volcanic activity on Kamchatka during the Holocene. That pulse produced 245 – 292 km3 of eruptive products.
Volcano and Eruptions
Diky Greben was formed shortly after the KO eruption and caldera collapse. It erupted rhyodacite and dacite with a bit of andesite. These products differ chemically from the KO eruption products. The volcano itself is a large, extrusive massif with a main dome, multiple smaller domes, associated ignimbrites, lava flows, and large landslide deposits. It was formed immediately W of the KO caldera rim. Initial pumice fall deposits from Diky Greben are on top of the KO ignimbrite as is an ignimbrite. The time between the Diky Greben and KO eruptions was too short to allow any soil formation, perhaps less than a century.
It is the largest modern volcano with silicic rocks in the Kurile – Kamchatka island arc. Multiple domes and lava flows of rhyodacite (5 km3), dacites (8 km3), and andesites (2 km3) were erupted. The volcano has a small amount of pyroclastic breccias. The main center of eruption is the highest point of the volcano – Mount Nepriyatnaya (Unpleasant), a partly broken extrusive dome. Large rockfalls from the dome occur annually, leading to some speculation that the dome is still growing.
Diky Greben formed in three episodes: 7.5 ka; 4.2 ka; and 1.6 ka, with a 3 ka repose period between activity. The volcano occupies over 100 km2 with a volume over 15 km3. Oldest rocks are rhyodacites, 75 – 80% of the volcanic history. Dacites and andesites, the largest part of the volcano, were erupted the last 2 – 1.5 ka, 25 – 20% of the volcano’s history. Volcanic activity has increased over the last 2 – 1.5 ka.
There are four confirmed eruptions, with the most recent 350 AD. It ejected 9 – 10 km3 of dacite and 2 – 3 km3 of andesitic lavas and tephras. The eruption left two craters and smaller vents and produced a tephra deposit, several lava domes, and a greater than 350 m thick, 4 km long lava flow to the south with marginal levees, pressure ridges and coulees. Previous eruptions were 2250 BC, 3050 BC and 5700 BC, with the oldest one immediately following the formation of the Kurile Lake caldera.
Diky Greben has landslide deposits unique in Kamchatka. E and N of the main dome are two large lava bodies created by sector collapse of the dome. The eastern body contains huge dome chunks forming specific steps toward Kurile Lake. It was stopped by an older dome. The northern lava body is 8 km long, over 200 m thick with a volume 4 – 5 km3. It appears to be a blocky lava flow with marginal levees and ridges. Unlike those features in a regular lava flow, these are arrayed against the direction of motion. The farthest part of the deposit appears to be hummocky typical of a debris avalanche. The suspected collapse scar on the northern side of the main dome is a 700 m steep slope with talus at its foot.
Quite a few blocks of Diky Greben rhyodacite measure 2-5 to 40 m across, mixed with smaller debris are scattered up to 2 km NE of the nearest dome. All of these blocks are cracked, suggesting a hard landing as they bounced and rolled their way down the slope.
Most observations suggest a collapse origin for both the northern and eastern lava bodies. Some of the northern bodies’ features suggest an initial lava flow early in the eruption that was overridden by a debris avalanche. This deposit has large lava chunks without any sandy matrix and the degree of fragmentation increases with distance from the source being highest toward the end of the flow.
Collapse deposits are only covered by moderate tephra falls, suggesting the domes were not sufficiently pressurized to produce a large eruption. There is speculation that these sector collapses took place sometime after the main dome building stage.
We covered Kamchatka tectonics in a 2015 post. That post would be a good starting point for inital review.
The short form of Kamchatkan tectonics is the subduction of the Pacific Plate under the Okhotsk Plate (or block). The volcanic front consists of volcanic arc subduction volcanoes. The Kuril Kamchatkan Trench offshore to the east is the subduction zone. The subducted Pacific Plate provides mantle fluids powering volcanic activity in Kamchatka and south along the Kuril Islands.
As a subduction zone, the entire region is subject to massive megathrust earthquakes. There was a M 8.3 in 1737, a M 8.5 in 1923, a M 8.2 inn 1952, a M 8.2 in 1959, and a M 7.6 in 2006.
The Diky Greben / Kuril Lake Caldera region is an example of a dangerous, albeit remote volcanic region. Over the last half million years, it created two calderas, multiple stratovolcanoes, and erupted nearly 300 km3 of material. Recent volcanic activity took place at Zheltovsky in 1923, Illinsky in 1901, Kosheleva and probably Kambalny in the 17th Century. Volcanoes here are subject to flank collapse and debris avalanche. The area is wet, so any eruption will have ample opportunity to interact with water, snow or ice, increasing the violence of whatever is taking place. While these systems typically have a long repose time between eruptions, we may be entering a more active period. Finally, there is a low velocity zone beneath the Kurile Lake Caldera.