Black Peak is an eroded stratovolcano and dome complex constructed in an ice-free caldera on the Alaska Peninsula some 725 km SW Anchorage.  The caldera is at the W end of a T-shaped group of mountains along the E coast of the Alaska Peninsula that measures 22 x 45 km. 

The area is sparsely populated with less than 500 within 100 km of the volcano complex.  As such, it has not been closely studied in the 45 years since it was identified as a volcano. 

The closest village is Chignik Bay (Chignik), located 38 km SE from Black Peak.  Chignik Bay, Chignik Lake and Chignik Lagoon are three small, remote native villages in the region.  They are separated by some 24 km.  There are no connecting roads, so all travel is done either by air or water.  Chignik Bay is part of the Alaska Marine Highway System with service spring – fall before the weather gets too bad.

Chignik comes from the Aleut word for “big wind.”  The area was initially populated by Kanaigmuit and Aleuts.  They were dependent on the sea, living on otter, seal, porpoise and whale.  Russians showed up sometime in the 18^th Century.  There was a Russian fur boom 1767 – 1786 that decimated the otter population.  Disease and warfare over this time cut the native population in half.

Commercial salmon became prized within two decades after Alaska was purchased from Russia in 1867 and a commercial fishing activity grew that eventually included processing.  Additional Europeans moved into the region with the canning activity.  There was coal mining in the area 1899 – 1915. 

Today, the region is populated by a mix of Scandinavian and Russian – Aleuts.  While the cannery no longer exists, the local economy is largely supported by commercial fishing for Pacific cod, halibut and salmon.  Local governance is done by the Chignik Lagoon Village Council.  Permanent population is perhaps 70, which during fishing season swells to the 600 – 800 people who work on the trawlers and processing plant.  It is politically part of the Lake and Peninsula Borough, Alaska. 

Climate is considered as a subarctic climate, though mild due to its proximity to the Pacific Ocean.  Average temperatures run 7° – 0° C, with an average precipitation of over 210 cm/yr.  Most of this is rain, as only 12 cm of snow falls. 

Black Peak is not actively monitored, though Alaska Volcano Observatory has active, real-time monitoring including webcams at neighboring Aniakchak and Veniaminof. 

Region

One of the striking features of this part of the Alaska Peninsula is the alignment of three calderas, Veniaminof, Black Peak and Aniakchak, from SW to NE along the peninsula.  All three of these are separated by about 50 km.  All three had their last caldera forming eruption 4.6 – 3.4 ka, with Black Peak being the oldest. The two larger systems, Veniaminof and Aniakchak are considered active, with multiple eruptions since their last major one.  In contrast, following the caldera forming eruption, Black Peak extruded at least a dozen dacite domes and a few lava flows after the caldera forming eruption.  Products of the post caldera activity mostly filled the caldera.  There has been no recent activity at Black Peak, though there are some gas emissions. 

There are additional volcanoes to the SW of Veniaminof and NE of Aniakchak.  The group SW around Stepovak Bay is particularly closely spaced and recently active.   Distances in the following section are measured from Black Peak.  Note that distance between volcanoes along this segment start out 50 km apart until you get to the closely spaced Stepovak Bay Group 100 km SW. 

Over the years, we published multiple pieces on the two major volcanic centers in the region, Veniaminof 2014, 2015,  and Aniakchak, 2013.  There was a 2015 survey of Alaskan calderas that touched on both systems.  We have not revisited them in recent years, though Veniaminof continues to be one of the most active Alaskan volcano with its last eruption 2021 – 2022. 

Yantarni

Yantarni is a 1,345 m andesitic stratovolcano located between Aniakchak and Chigniadak, 110 NW from Black Peak.  It was not identified as a volcano until 1979, though the peak was named by Russians on a navigation chart.   The volcano is named after nearby Yantarni Bay and Creek.  There is an abundance of amber (yantar in Russian) found in the area.

The volcano has a volume of 3.5 km3 and is located near a fault with previous magma activity.  The current cycle of activity began somewhere in the last 1.2 Ma.  Initial activity erupted andesitic lava flows possibly from multiple vents.  The cone was breached 3.5 – 2.0 ka likely with a directed blast eruption similar to Mount St Helens.  The eruption also produced a debris avalanche.  The eruption was followed by dome extrusion and multiple pyroclastic flows.  These extend some 4 km with a volume of around 1 km3.

The volcano erupted several different compositions of magma in small volumes.  It does not appear to have a large, shallow magma chamber. 

Aniakchak

Aniakchak is a 10 km diameter, ice-free, circular caldera located 54 km NE from Black Peak.  It is a maximum of 1 km deep and is drained by a river through a break in the caldera wall.  Surprise Lake, a 3.2 km long caldera lake hosts a run of red salmon that recolonized the lake and river following the last major eruption 3.4 ka. 

Post caldera activity built numerous domes, lava flows and pyroclastic cones on the floor of the caldera.  Vent Mountain is the largest of these, 2.5 km in diameter, 430 m above the caldera floor.  The remaining ancestral cone outside the caldera rim is deeply eroded by numerous glaciers that cut U-shaped valleys into the slopes before the series of caldera-forming eruptions. 

The oldest post glacial caldera forming eruption was a VEI 6.5 some 8.3 ka that ejected at least 30 km3 bulk volume.  It was followed by the largest caldera-forming eruption, 5.4 ka.  This one was a VEI 6.8, ejecting 50 km3 of material.  Prevailing winds put centimeters of ash on today’s Prudhoe Bay oilfields and into the Arctic Ocean, over 1,500 km N of the volcano.  There were a pair of VEI 4.9 and VEI 4.6 eruptions in 1531 AD and 1931.  Both of these came from cones in the caldera. 

The oldest caldera forming eruption (not listed in the VOGRIPA database) was andesitic, depositing nonwelded ignimbrite in valleys below the volcano and welded flows higher on its flanks.  The subsequent Plinian eruption 7.0 ka came from a vent NE from the ancestral summit deposited the Black Nose Pumice.  This began with a rhyodacitic lava, pumice fall, and Plinian welded ignimbrite.  Final layers were dacite pumice fall and NW flank lava flow.  There were at least 20 additional eruptions between this one and the largest one 3.4 ka.

The 5.4 ka caldera forming eruption produced ash flows that reached the Pacific Ocean on both sides of the Alaska Peninsula.  The flows are typically unwelded, filling glacial valleys to a depth of at least 75 m near the rim.  The flows were highly mobile, cresting 260 m high passes in the Aleutian Range.  They are found up to 50 km from the caldera rim.

Post caldera vents are located mainly on caldera ring fracture system.  Early activity extruded small dacite domes into a deep caldera lake and a lava flow on the NW flank.  Three andesitic to basaltic andesitic tuff cones were constructed on the caldera floor after catastrophic draining of the crater lake lowered its surface by at least 200 m.  Dacite andesitic activity at Vent Mountain and Half Cone began perhaps 1,000 AD.  Half Cone produced a Plinian eruption around 1600 AD.  This dacite covered earlier andesitic fall deposits.  Blocky Cone was built by Strombolian activity after Half Cone and Vent Mountain. 

The most recent eruption in 1931 produced a dacite – rhyodacite tephra followed by a large andesitic tephra.  The eruption ended with a minor basaltic andesite.

Veniaminof

The massive Mount Veniaminof is a 2,507 m tall stratovolcano topped by an 8 x 11 km ice-filled caldera.  It is located some 55 km SW from Black Peak.  The caldera was formed by a VEI 6.7 eruption some 4.3 ka that ejected 50 km3 of dacite.  Since the climatic eruption, ice filled the caldera.  All historic eruptions have taken place at a cinder cone in the middle of the caldera whose peak rises above the ice.  Like all other volcanoes in this part the Alaska Peninsula, Vemiaminof is located in a sparsely populated part of the Alaska Peninsula.

Veniaminof is one of the largest and most active volcanoes in the Aleutian arc.  It has a base diameter of 40 km with an estimated volume of 350 km3.  The caldera walls reach 2,500 m.  There are widespread glassy lava flow breccias, columnar joining, ice-marginal flows and tuyas indicating extensive ice – lava interaction.  The volcano mostly erupted basalts to basaltic andesites 250 – 100 ka.  These are visible on the S and W flanks.  Andesites and dacites were erupted as recently as 36 ka from a line of NW-trending vents on the flank. 

The first known caldera collapse took place sometime before 28 ka, the date of basaltic andesitic lavas that covered it.  Eroded lavas with ice contact joining drapes the rim of the caldera, indicating a caldera was present 12 ka.  The youngest Veniaminof lavas on the S side of the caldera date 50 ka.  A few cinder cones on the flank may also date around 12 ka.  There are no debris avalanche deposits found around the volcano that would provide an alternate sector collapse explanation for the origin of the caldera structure.

Two massive andesitic eruptions 4.7 and 3.7 ka produced pyroclastic flows on the flanks and into the surrounding valleys.  The younger of these emplaced lithic breccias at higher elevations.  There is a younger widespread sub-Plinian dacite fall up to 30 cm thick.  This suggests that the long-lived system may produce silicic eruptions in addition to historic basaltic andesitic strombolian and effusive eruptions from the intracaldera cone(s).

Large lahars were ejected during the 3.7 ka V2 eruption.  They flowed up to 50 km from the volcano.  Deposits from these are found in all glacial valleys and are 10 – 15 m thick.  Lahar deposits cover 800 – 1,000 km2.  They record substantial inundation of the major valleys on all flanks of the edifice.  Significant water is necessary to produce lahars of this size, meaning an ice-filled summit probably existed during this eruption. 

All 24 historic eruptions 1830 – present came from the 300 m high intracaldera cinder cone (Cone A).  It is a kilometer in diameter with a volume around 0.1 km3.  Historic eruptions have been small to moderate Strombolian explosions, occasional small lava flows, and lava fountaining.  Plumes from these eruptions are typically small, 4 – 6 km above sea level. 

The caldera icefield is a level, flat surface.  Only Cone A has significant relief above the ice and snow.  it is typically ice and snow free year-round.  Cone B is under construction.  There are at least three more cinder cones above the ice surface along the S margin of the icefield.  These look fresh and are not obviously glaciated.  It is possible that one or more of these were historically active.  Actual eruptive history of these cones is unknown. 

The icefield measures around 290 km2 with an estimated volume of over 14.5 km3.  8 km3 of it is in the caldera.  Parts of the caldera icefield may be frozen to the caldera floor.  Due to the ice-filled caldera, there is no small concern that future eruptions will destabilize the caldera ice field, releasing jokulhlaups (glacial outburst floods) through openings in the rim and down the flanks.  24 historic eruptions since 1830 including at least four VEI 3’s haven’t caused any of these.  While lava during historic eruptions melts ice, cauldrons and ice melt pits are localized close to the site of the eruption. 

Kupreanof

The 1,895 m Kupreanof is the largest and most NE of a group of five relatively closely spaced volcanic centers W of Stepovak Bay.  It is located 87 km SW from Black Peak.  Both Smithsonian GVP and AVO lists it as part of the Stepovak Bay Group.  There is a debris flow or possible block and ash flow into a glacial valley S of the volcano.  The current volcano has vigorous fumarole activity.  There was a 1987 pilot report of an “ash horizon” extending some 15 km N after emissions from a solfatara field on the SSW flank. 

There is a fault NW of Kupreanof and the rest of the Stepovak Bay Group that vertically offsets the volcanoes from earlier flows. 

Stepovak Bay Group

The Stepovak Bay Group is an 18 km long string of four cones just SW from neighboring Kupreanof, 104 km SW from Black Peak.  AVO has them listed as Stepovak Bay 1-4.  Stepovak Bay 1 is the oldest at the SW end of the chain.  It dates 530 – 400 ka.  Stepovak Bay 2 is a cinder cone with recent (last 10 ka) andesitic lava flow extending NE to SE.  Setpovak Bay 3 is a cinder cone with a thick recent lava flow its ice-filled 300 m ice filled crater.  It entered the same valley as the lava flow from Stepovak Bay 2.  Stepovak Bay 4 is closest to Kuprenof.  It is a small stratovolcano with debris flows or block and ash flows.  These have been obscured by the permanent ice cap.  Stepovak Bay 4 also has the occasional observed fumarole.   

Stepovak Bay 2 and 4 show evidence of eruptions over the last 10 ka.  These eruptions put small debris flows into neighboring glacial valleys.  Stepovak Bay 1 and 3 do not show this sort of recent activity.  They also have ice-filled summit craters, 500 m wide with Stepovak Bay1 and 300 m wide for Stepvak Bay 3.  The lava flows extend to near sea level.  Note that Stepovak Bay 1-4 are informal names for unnamed volcanoes in this group.

There is a fifth area of relatively recent flows (lava, debris and pyroclastics?) that may be an unrecognized eruptive center.  There are rocky outcrops in the snowfield that may be parts of the underlying edifice.  The S centers are built on thick tuff deposits of uncertain age. 

Black Peak

Black Peak is a group of at least a dozen resurgent dacite domes and a few lava flows populating a 3.5 km diameter caldera.  The highest of these tops out at 1,032 m.  The caldera forming eruption took place 4.6 ka, filing Ash Creek and Bluff Creek valleys to the W and N with as much as 100 m of ignimbrite.  The dome complex, lava flows and block and ash flows are centered in the S part of the caldera.  There are two crater lakes in the caldera. 

Initial satellite study of Black Peak in 1991 identified a caldera with at least four domes / lobes.  The magmatic center of activity migrated W over time.   Field studies took place around 2003.  There is not a lot published about Black Peak. 

The volcano erupts andesites, basaltic andesites and dacites.  Most of the domes are similar in age, post caldera, and are constructed with extruded dacite to andesite magma.  Older domes tend toward dacite while younger tend to andesite.  Most are contained within the caldera, though several spill out onto the SE flank.  The domes and flows after caldera formation vary in composition, hydrothermal altering, erosion and vegetation.  They are covered with grasses and lichens below 900 m.  Above that line, they show more freeze thaw fractures and weathered surfaces. 

There is widespread alteration of older rocks suggesting an active hydrothermal system that is no longer present.  There are also weathered and altered outcrops along the caldera walls and outside the rim.  Some of these are altered volcanic necks and pre-caldera domes.

One of the two intracaldera lakes shows signs of overturning and rapid fluctuations in dissolved gasses.  There are terraces, dry channels and lake clay exposures that indicate that at least two of the multiple small lakes inside the caldera today were once part of a larger body of water. 

Activity at Black Peak is informally divided into three periods:  pre-caldera, post-caldera and recent.  Domes and volcanic necks formed before the caldera eruption are cut by the caldera rim.  They are older than all other eruptive products and show extreme alteration and weathering. 

The Black Peak caldera terminates a highly altered volcanic edifice.  It has been refilled with lava domes, minor lava flows, and pyroclastics.  There are significant fall deposits from the eruption forming a distinct regional tephra called the “salt and pepper ash.”  Soils below the ash flow deposit are dated 4.6 ka, which has been assigned to the date of the eruption.  The salt and pepper ash is found interlayered with the two caldera forming eruptions at Aniakchak in the area between the two systems. 

Pyroclastic flows from the eruption fill two major drainages around the caldera to a depth of 100 m.  They extend at least 10 km from the caldera rim.  There is a smaller, lower crystal rich dacite flow unit capped by a lithic-rich unit.  Volume is estimated at less than 10 – 20 km3, though VOGRIPA carries this eruption at a full 30 km3 assigning it a VEI 6.5. 

Post-caldera resurgent activity built the central domes, following the caldera eruption.  These are the oldest domes following the eruption.  They have extensive freeze-thaw fractures.  There is a marked decrease in silica content of the magma over time.  Some domes show evidence of magma mixing as more juvenile magma enters a shallow dacite magma chamber.  Magma of the extruded domes did not have much variation in gas content.  A dome N of the central depression has three different rock types.  This is thought to be due to variations in cooling rates during dome emplacement. 

There are no coarse tephras from dome emplacement, though there are thick, fine-grained, highly altered ash fall deposits found on the caldera rim.  These cover ash flow deposits from caldera formation indicating dome emplacement closely followed caldera formation. 

The most recent activity extruded domes at the S margins of the central dome complex.  These domes have no altered rocks.  They have significant flow ridges, creases and spine features on the surfaces.  These features indicate flow direction.  There is at least one coulee.  Several domes collapsed over the E rim forming block and ash flows that extend 1.5 km down Red Bluff Creek.  Age of these deposits is somewhere around 1500 AD.  There is an avalanche region around the SE dome that supports widespread soil and vegetation.  Many of the recent domes along the margin of the complex have flow structures and collapse features. 

There are no reports of eruptive activity at Black Peak since 1750 AD.  There is a 1926 USGS report of CO2 and H2S springs within the caldera.  Today, while there are a few areas of diffuse bubbling, there are no significant sites of hot or warm volcanic degassing.  There is an area of sulfur deposition against the W inner caldera wall that is not thermally active. 

Tectonics

Tectonics of the Alaska Peninsula is driven by the continuing subduction of the Pacific Plate under the North American Plate.  The subduction trench is some 350 km offshore to the SE.  The Pacific Plate subducts shallowly, perhaps 100 km beneath the crest of the Alaska Peninsula as it changes its subduction angle steeply into the mantle.  Water-rich molten rock from the subduction finds its way to the surface powering volcanic activity along the peninsula. 

This collision has been going on since at least the Mesozoic, as the moving Pacific Plate plastered multiple terranes onto the southern side of Alaska constructing the bulk of the state.  The most recent arrival was the Yakutat Terrane, its accretion starting 25 Ma and ongoing today.  The Alaska Peninsula is constructed by a pair of what are described as subterranes, the Chignik and Iliamna subterranes.  The subterranes are separated by the Bruin Bay Fault system N of Becharof Lake.  The suture line is not so well-defined S of that point. 

Volcanic activity along the peninsula has likewise been going on for a very long time with the remains of earlier volcanoes being altered, eroded, and otherwise changed over tens to hundreds of million years of action by water and ice.  Newer volcanic systems were built upon this basement.  

As with all other subduction regimes, the ongoing subduction drives massive megathrust earthquakes and volcanic activity.  Volcanoes in this part of the Alaska Peninsula are typically spaced 40 – 50 km apart.  There are locations where discontinuities in the underlying crust encourage multiple closely spaced volcanoes.  The Katmai – Novarupta region is one example.  Stepovak Bay is another.  Black Peak is located on the Chignik subterrane which is the most W and S of the two subterranes. 

Conclusions

Black Peak is a currently dormant volcanic system.  It shows signs of past vigorous volcanic activity including caldera formation, resurgent dome extrusion, and extensive hydrothermal altering of its rocks.  The system is not currently active.  Hydrothermal activity appears to have also subsided, though there are some cool gas emissions.  Its neighboring caldera systems at Veniaminof and Aniakchak are both recently active.  The subduction continues, so there should be a continuing supply of magma below it.  What future injections of hot, juvenile magma into a crystalizing dacite magma chamber may do is anyone’s guess as we have not yet characterized the nature of the shallow magma chamber. 

Additional information

Black Peak, Smithsonian GVP 

Alaska Volcano Observatory, Black Peak

Analysis of composition and chronology of dome emplacement at Black Peak volcano, Alaska utilizing ASTER remote sensing data and field-based studies, UAF Thesis, JN Adelman, May 2005

Black Peak caldera, Alaska:  preliminary investigations of the ~ 4600 BP caldera-forming eruption and subsequent post-caldera activity, McGimsey, et al, Dec 2003

Stratigraphic framework of the Alaska Peninsula, Chapter A, Detterman, et al, USGS Bulletin 1969-A, 1996

Holocene tephra stratigraphy on northern Kodiak Island, Alaska, TG Tannenbaum, 1996

Quaternary volcanism in the Alaska Peninsula and Wrangell Mountains, Alaska, Miller & Richter, Jan 1994

Geothermal resources of the Aleutian Arc, Motyka, et al, State of Alaska, Department of Natural Resources Professional Report 114, 1993

Maps showing interpretation of Landsat imagery of the Chignik and Sutwik Island quadrangles, Alaska, Miscellaneous field studies map 1053- O, LeCompte & Steele, 1981

Gravity anomaly and interpretation map of the Chignik and Sutwik island quadrangles, Alaska, Case, et al, 1981

Past volcanic activity in the Aleutian Arc, USGS Alasan volcano investigations, Report No 1, RR Coats, 131729

Postglacial eruptive history, geochemistry and recent seismicity of Aniakchak volcano, Alaska Peninsula, USGS Professional Paper 1810, Bacon, et al, USGS, 2014

History and eruptive style of Mount Veniaminof, a huge Alaskan basalt to dacite volcano with Pleistocene and Holocene caldera-forming eruptions, Bacon, et al, Dec 2003

Simultaneous effusive and explosive cinder cone eruptions at Veniaminof volcano, Alaska, C Waythomas, USGS, AVO, Dec 2021

Alaska Volcano Observatory Veniaminof

Geologic framework of the Alaska Peninsula, southwest Alaska, and the Alaska Peninsula Terrane, USGS Bulletin 1969-B, Wilson, et al, 2015