Hannegan caldera

Last updated December 12, 2023

Hannegan caldera is a 3.72 million year old volcanic collapse structure in the North Cascades of the U.S. state of Washington.^[2] The caldera collapsed during two separate volcanic eruptions that produced as much as 140 km³ of rhyolite ash.^[3]^[4]

The caldera is filled with 55-60 km³ of tuff consisting of ignimbrite,^[5] wall-rock breccia,^[6] and post-caldera sedimentary rocks.^[7] Rocks filling the caldera are lumped into a stratigraphic unit called the Hannegan volcanics.^[8]^[9] This geologic unit is subdivided into the ignimbrite of Hannegan Peak, which is overlain by the slightly younger ignimbrite of Ruth Mountain. Hannegan caldera is centered 8.9 km northeast of Mount Shuksan.^[10] Prominent geographic points within the caldera include Hannegan Peak, Hannegan Pass, Ruth Mountain, Icy Peak, the western portion of Copper Ridge and the uppermost reaches of the Chilliwack River. The caldera’s western margin is in Mount Baker-Snoqualmie National Forest but most of the structure is in North Cascades National Park. The caldera is traversed by portions of the Hannegan Pass,^[11] Hannegan Peak,^[12] Chillwack River,^[13] Copper Ridge, and Boundary trails, but most of it is in untracked and rugged mountainous terrain. It is among the best exposed and youngest trap door calderas in the world, and is believed to be the only described double trapdoor caldera on Earth.^[2]^[14]

Geologic history

Pre-caldera volcanism and topography

The entire region has been deeply eroded by repeated continental and alpine glaciations. No volcanic structures or rocks predating caldera collapse survived multiple glaciations and collapse of the caldera. However, the presence of volcanic rock fragments within the intracaldera tuff are evidence for pre-caldera volcanism, as are dikes outside the caldera margin that have geochemical compositions distinct from rocks related to caldera collapse and later volcanism within the caldera.^[1]^[15]^[16]

First caldera collapse

Around 4 million years ago large volumes rhyolitic magma rose high into the crust. This intrusion most likely caused the surface to dome upwards. Fractures caused by this deformation may have provided conduits for some magma to reach the surface and erupt into relatively small volcanic structures such as felsic and intermediate lava flows and domes, cinder cones, and perhaps small stratovolcanoes. Over 10s or 100s of thousands of years, this upward deformation eventually resulted in a semicircular fracture, or ring fault to form in the brittle crust.^[2] This fault encircled the northern margin of the uplifted area and reaching down to the magma chamber, causing sudden release of confining pressure on the magma. Consequently the magma erupted huge volumes of magma as towering columns of volcanic ash and pumice, as well as pyroclastic flows. As the magma emptied, the surface collapsed in a trapdoor fashion down to the north, with the hinge on the south.^[14] Though no longer preserved due to millions of years of intense erosion, searing pyroclastic flows must have swept for 10s of kilometers down river valleys beyond the margins of the caldera, incinerating everything in their path. As the surface subsidized a kilometer or more during eruption, volcanic ash filled the resulting horseshoe-shaped caldera. Rock outside the ring fault slid inward as large landslides and left lenses of wall rock breccias and megabreccia interbedded in the tuff filling the collapsing caldera. This tuff, erupted in a single eruption, was lithified and is preserved as the ignimbrite of Hannegan Peak; it is at least 900 meters thick with no base is exposed.^[17]^[9] It is confined within the northern half of the caldera’s structural margin. A relatively precise ⁴⁰Ar/³⁰Ar radiometric age dates this unit to 3.722 +/- 0.020 million years ago.^[2] This northern portion of the Hannegan caldera is confined to the area between Ruth Mountain and Hannegan Peak, and includes the upper most portion of the Chilliwack River valley.

Hiatus and sedimentation

Collapse probably took place over a few days. At some time, a lake formed in the depression, and fine grained sediment was deposited on its floor, preserved on the northern flank of Ruth Mountain today as shale and sandstone. These rocks contain fossil leaves, and remain undated.

Second caldera collapse

A large volume of unerupted magma remained within the crust, and may have been augmented by subsequent intrusions. After only a brief interval, continued deformation caused the northern ring fault to propagate southward to form an oblong oval above the remaining magma, which again erupted in another cataclysmic eruption. The southern portion of the caldera then collapsed, this time in a down-to-the-south trapdoor fashion. This formed a ‘double-trap door caldera’, a unique geologic structure. The second portion of the Hannegan collapse was filled with the ignimbrite of Ruth Mountain, exposed from the northeast flank of Ruth Mountain to the southeast flank of Icy Peak to the south. The Ruth Mountain ignimbrite contains many clasts of volcanic rock that predates caldera collapse. This unit must have covered the northern portion of the caldera as well, but was stripped away in that section by erosion. No rock suitable for dating has been found in this unit.

Post-collapse pluton intrusions

Two granodiorite magma bodies invaded the Ruth Mountain ignimbrite, and are exposed today as a pair of plutons on Icy Peak and the eastern wall of Nooksack Cirque. The older of these granitic masses is dated to 3.42 million years old, and therefore confines the rock filing the second episode of caldera collapse to the geologically brief 300,000 thousand year interval between the Hannegan ignimbrite (3.72 million years) and 3.42 million years for the pluton. It is likely the Ruth Mountain ignimbrite is much closer to the older age. The second small pluton closely followed, and is 3.36 million years old. Both are part of the Chilliwack Batholith.^[8] Mineral analyses from these plutons indicate they cooled at least 1 km below the surface. Yet they are both exposed today due to erosion. They outcrop at the summit of Icy Peak (2156 m) and to within a few hundred feet of the summit of Ruth Mountain (2169 m), the highest point within the caldera. This indicates profound erosion of at least 1 km of intracaldera volcanic rocks in the 3.36 million years since intrusion of these plutons, including any volcanic deposits that may have been associated with the plutons.^[18]

The end of volcanic activity in the caldera

Dikes and small rhyolite pods intruded the intracaldera tuff after the caldera collapse was complete. A few small outcrops of andesitic rock are scattered within the caldera, the remnants of lava flows. One sequence of three lava flows exposed on the ridge crest between Ruth Mountain and Chilliwack Pass has a preserved thickness of 240 meters and is dated to 2.96 +/- 0.30 million years old.^[2] It is the youngest dated rock unit within the Hannegan volcanics. Following the end of magmatism in the Hannegan area, the focus of magma intrusion and volcanism migrated to the southwest, and sequentially emplaced the Lake Ann Stock (2.75 million years old),^[19]^[20] Kulshan caldera (1.15 million years old),^[21] and the numerous vents in the Mount Baker Volcanic field,^[22] including the currently active Mount Baker itself.

Comparison with other Cascades calderas

The few known Cascade calderas are small and erupted relatively small volumes of ash and ignimbrite.^[23]^[24] Hannegan caldera is only 8 x 3.5 km in outline, with a calculated eruption volume of 55-60 cubic km of magma. Only three calderas have formed in the Cascades since the collapse at Hannegan, and each erupted about the same volume of magma as Hannegan. The Kulshan caldera (1.11 million years old)^[21] is 4 x 8 km. The best known and youngest Cascade Range caldera is at 7700 year old Crater Lake, 8 x 10 km.^[25]^[26] The little known 600,000 year old Rockland caldera^[27]^[28] underlies Lassen Peak volcanic center. It is 600,000 years old and is estimated to measure 6 x 6 km. Two other much older Cascade calderas have been sufficiently described in the geologic literature to include here. These are the 21 million-year-old Coquihalla caldera east of Hope, British Columbia, (approx 6 x 6 km)^[29] and the 25 million year old Mount Aix caldera (6x9 km)^[30]^[31] 40 km east of Mount Rainier.

Related Research Articles

A caldera is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is gone. The ground surface then collapses into the emptied or partially emptied magma chamber, leaving a large depression at the surface. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. Compared to the thousands of volcanic eruptions that occur each century, the formation of a caldera is a rare event, occurring only a few times per century. Only seven caldera-forming collapses are known to have occurred between 1911 and 2016. More recently, a caldera collapse occurred at Kīlauea, Hawaii in 2018.

Mount Baker, also known as Koma Kulshan or simply Kulshan, is a 10,781 ft (3,286 m) active glacier-covered andesitic stratovolcano in the Cascade Volcanic Arc and the North Cascades of Washington in the United States. Mount Baker has the second-most thermally active crater in the Cascade Range after Mount St. Helens. About 30 miles (48 km) due east of the city of Bellingham, Whatcom County, Mount Baker is the youngest volcano in the Mount Baker volcanic field. While volcanism has persisted here for some 1.5 million years, the current volcanic cone is likely no more than 140,000 years old, and possibly no older than 80–90,000 years. Older volcanic edifices have mostly eroded away due to glaciation.

A supervolcano is a volcano that has had an eruption with a volcanic explosivity index (VEI) of 8, the largest recorded value on the index. This means the volume of deposits for such an eruption is greater than 1,000 cubic kilometers.

The Bishop Tuff is a welded tuff that formed 764,800 ± 600 years ago as a rhyolitic pyroclastic flow during the approximately six day eruption that created the Long Valley Caldera. Large outcrops of the tuff are located in Inyo and Mono Counties, California, United States. Approximately 200 cubic kilometers of ash and tuff erupted outside the caldera.

<span class="mw-page-title-main">La Garita Caldera</span> Large caldera in the state of Colorado, U.S.

La Garita Caldera is a large caldera in the San Juan volcanic field in the San Juan Mountains around the town of Creede in southwestern Colorado, United States. It is west of La Garita, Colorado. The eruption that created the La Garita Caldera is among the largest known volcanic eruptions in Earth's history, as well as being one of the most powerful known supervolcanic events.

The Cascade Volcanoes are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 miles (1,100 km). The arc formed due to subduction along the Cascadia subduction zone. Although taking its name from the Cascade Range, this term is a geologic grouping rather than a geographic one, and the Cascade Volcanoes extend north into the Coast Mountains, past the Fraser River which is the northward limit of the Cascade Range proper.

This timeline of volcanism on Earth includes a list of major volcanic eruptions of approximately at least magnitude 6 on the Volcanic explosivity index (VEI) or equivalent sulfur dioxide emission during the Quaternary period. Other volcanic eruptions are also listed.

The Canadian Cascade Arc, also called the Canadian Cascades, is the Canadian segment of the North American Cascade Volcanic Arc. Located entirely within the Canadian province of British Columbia, it extends from the Cascade Mountains in the south to the Coast Mountains in the north. Specifically, the southern end of the Canadian Cascades begin at the Canada–United States border. However, the specific boundaries of the northern end are not precisely known and the geology in this part of the volcanic arc is poorly understood. It is widely accepted by geologists that the Canadian Cascade Arc extends through the Pacific Ranges of the Coast Mountains. However, others have expressed concern that the volcanic arc possibly extends further north into the Kitimat Ranges, another subdivision of the Coast Mountains, and even as far north as Haida Gwaii.

The San Juan volcanic field is part of the San Juan Mountains in southwestern Colorado. It consists mainly of volcanic rocks that form the largest remnant of a major composite volcanic field that covered most of the southern Rocky Mountains in the Middle Tertiary geologic time. There are approximately fifteen calderas known in the San Juan Volcanic Fields; however, it is possible that there are two or even three more in the region.

Calabozos is a Holocene caldera in central Chile's Maule Region. Part of the Chilean Andes' volcanic segment, it is considered a member of the Southern Volcanic Zone (SVZ), one of the three distinct volcanic belts of South America. This most active section of the Andes runs along central Chile's western edge, and includes more than 70 of Chile's stratovolcanoes and volcanic fields. Calabozos lies in an extremely remote area of poorly glaciated mountains.

David Samuel Tucker is a geologist, author, and union organizer in Washington state. He is a research associate at Western Washington University. He was an instructor at North Cascades Institute, and the director of the Mount Baker Volcano Research Center. He writes the blog Northwest Geology Field Trips, a blog aimed at laypeople detailing where to find interesting geology in the Pacific Northwest. In 2015, he published a popular book on Washington geology, Geology Underfoot in Western Washington. He resides in Bellingham, Washington. In the 1980s he worked as a mountaineering guide in the Cascades, Mexico, and South America.

Cerro Guacha is a Miocene caldera in southwestern Bolivia's Sur Lípez Province. Part of the volcanic system of the Andes, it is considered to be part of the Central Volcanic Zone (CVZ), one of the three volcanic arcs of the Andes, and its associated Altiplano-Puna volcanic complex (APVC). A number of volcanic calderas occur within the latter.

Kari-Kari is a Miocene caldera in the Potosi department, Bolivia. It is part of the El Fraile ignimbrite field of the Central Volcanic Zone of the Andes. Volcanic activity in the Central Volcanic Zone has generated 44 volcanic centres with postglacial activity and a number of calderas, including the Altiplano-Puna volcanic complex.

Ruth Mountain is a 7,115 ft (2,170 m) Skagit Range summit located two miles south of Hannegan Pass in the North Cascades of Washington state. The name honors Ruth Cleveland, daughter of President Grover Cleveland. This mountain's name was officially adopted in 1952 by the United States Board on Geographic Names. Ruth Mountain is situated on the shared border of North Cascades National Park and the Mount Baker Wilderness, which is part of the Mount Baker-Snoqualmie National Forest. The summit offers views of Mount Shuksan, East Nooksack Glacier, Seahpo Peak, Nooksack Tower, Icy Peak, Mount Sefrit, Mineral Mountain, and the Picket Range. The melting and receding Ruth Glacier on the north slope of Ruth creates the headwaters for the Chilliwack River. Precipitation runoff also finds its way into the Nooksack and Baker Rivers.

The Kulshan caldera is a Pleistocene volcano in the North Cascades of Washington and one of the few calderas identified in the entire Cascade Range. It is the product of the Mount Baker volcanic field, which has a history stretching back to possibly 3.722 million years ago.

Hannegan Peak is a 6,191-foot elevation (1,887 m) mountain summit located in the Skagit Range, which is a subset of the North Cascades in Whatcom County of Washington state. It is situated immediately north of Hannegan Pass, and 2.2 mi (3.5 km) north of Ruth Mountain in the Mount Baker Wilderness, which is managed by Mount Baker-Snoqualmie National Forest. Banning Austin and R.M. Lyle made the first ascent of Hannegan Peak in 1893 while surveying for a possible road across the Cascades over Hannegan Pass to Whatcom Pass. This peak was named in association with Hannegan Pass, which in turn was named for Tom Hannegan, State Road Commissioner at that time. Although no road was built, a four-mile trail leads hikers to the pass, and another one-mile path leads to the summit. Peaks which can be seen from the summit include Mount Shuksan, Ruth Mountain, Mineral Mountain, Mount Baker, Mount Sefrit, Mount Larrabee, Granite Mountain, Mount Chardonnay, Mount Rexford, the Picket Range, and many more.

The Bandelier Tuff is a geologic formation exposed in and around the Jemez Mountains of northern New Mexico. It has a radiometric age of 1.85 to 1.25 million years, corresponding to the Pleistocene epoch. The tuff was erupted in a series of at least three caldera eruptions in the central Jemez Mountains.

The Amalia Tuff is a geologic formation exposed in and around Questa, New Mexico. It has a radiometric age of 25.39 ± 0.04 million years, corresponding to the Oligocene epoch.

The Latir volcanic field is a large volcanic field near Questa, New Mexico, that was active during the late Oligocene to early Miocene, 28 to 22 million years ago (Ma). It includes the Questa caldera, in whose deeply eroded interior is located the Molycorp Questa molybdenum mine.

The Cascade Volcanic Arc is a chain of volcanoes stretching from southern British Columbia down to northern California. Within the arc there is a variety of stratovolcanoes like Mount Rainier and broad shield volcanoes like Medicine Lake. But calderas are very rare in the Cascades, with very few forming over the 39 million year lifespan of the arc.

References

1 2 3 Tucker, David S. (2006). "Geologic Map of the Pliocene Hannegan Caldera, North Cascades, Washington". Geological Society of America Digital Maps. doi:10.1130/2006.dmch003.
1 2 3 4 5 6 7 Tucker, D.; Hildreth, W.; Ullrich, T.; Friedman, R. (2007). "Geology and complex collapse mechanisms of the 3.72 Ma Hannegan caldera, North Cascades, Washington, USA". Geological Society of America Bulletin. 119 (3–4): 329–342. Bibcode:2007GSAB..119..329T. doi:10.1130/b25904.1. ISSN 0016-7606. S2CID 128417330. ResearchGate:249527328 USGS 70032860.
↑ Hildreth, Wes (2007). Quaternary Magmatism in the Cascades: Geologic Perspectives. U.S. Geological Survey Professional Paper 1744. ISBN 978-1-4113-1945-5.
↑ Haugerud, Ralph A.; Tabor, Rowland W. (2009). "Geologic Map of the North Cascade Range, Washington". U.S. Geological Survey Scientific Investigations Map 2940. Scientific Investigations Map. doi:10.3133/SIM2940. S2CID 128560085. NLA 4761905.
↑ "Mount Baker Volcano Research Center: Eruptive History". Mount Baker Volcano Research Center. Western Washington University . Retrieved 2022-12-11.
↑ Dragovich, Joe D.; Logan, Robert L.; Schasse, Henry W.; Walsh, Timothy J.; Lingley, Jr., William S.; Norman, David K.; Gerstel, Wendy W.; Lapen, Thomas J.; Schuster, J. Eric; Meyers, Karen D. (2002). "Geologic map of Washington—Northwest quadrant". Washington Division of Geology and Earth Resources Geologic Map GM-50. Washington State Department of Natural Resources. OCLC 50325812. Catkey:5683968 MIT Libraries docid:alma990020728850106761. In Schuster, J. Eric; et al. (2011). "Geologic Maps of Washington State" (PDF). Washington Division of Geology and Earth Resources Geologic Maps. Washington State Department of Natural Resources.
↑ Moen, Wayne S. (1969). "Mines and Mineral Deposits of Whatcom County, Washington" (PDF). Washington Division of Mines & Geology Bulletin. United States: Washington Department of Natural Resources. 57. OCLC 75702. OSTI 5309872. S2CID 128474733.
1 2 Staatz, Mortimer Hay; Tabor, Rowland W.; Weis, Paul L.; Robertson, Jacques F.; Van Noy, Ronald M.; Pattee, Eldon C. (1972). "Geology and Mineral Resources of the Northern Part of the North Cascades National Park, Washington". USGS Numbered Series Bulletin 1359. U.S. Geological Survey: 1-132. ASIN B000NEA2S8. doi: 10.3133/b1359 . LCCN 72600151. OCLC 768876024. Publication at the NPS History eLibrary. USGS b1359 EPA National Library:1303 309115 UNT key:ark:/67531/metadc304328.
1 2 Tabor, R. W.; Haugerud, R. A.; Hildreth, Wes; Brown, E.H. (2003). "Geologic Map of the Mount Baker 30- by 60-Minute Quadrangle, Washington". U.S. Geological Survey Miscellaneous Investigation Series (1 ed.). Menlo Park, CA: U.S. Geological Survey (I-2660). ISBN 0-607-96870-2.
↑ Hildreth, Wes; Lanphere, Marvin A.; Champion, Duane E.; Fierstein, Judy (2004-02-29). "Rhyodacites of Kulshan caldera, North Cascades of Washington: Postcaldera lavas that span the Jaramillo". Journal of Volcanology and Geothermal Research. 130 (3): 227–264. Bibcode:2004JVGR..130..227H. doi:10.1016/S0377-0273(03)00290-7. ISSN 0377-0273.
↑ "Hannegan Pass Trail 674". US Forest Service . Retrieved December 13, 2022.
↑ "Hannegan Pass and Peak". Washington Trails Association. Retrieved December 13, 2022.
↑ Olympic National Park (March 25, 2022). "Copper Ridge / Chilliwack River Trails". National Park Service .
1 2 Tucker, David S. (2008). "Two-phase, reciprocal, double trapdoor collapse at Hannegan caldera, North Cascades, Washington, USA". IOP Conference Series: Earth and Environmental Science. 3 (1): 012011. Bibcode:2008E&ES....3a2011T. doi: 10.1088/1755-1307/3/1/012011 . ISSN 1755-1315. S2CID 250683520.
↑ Mullen, Emily K.; Paquette, Jean-Louis; Tepper, Jeffrey H.; McCallum, I. Stewart (2018). "Temporal and spatial evolution of Northern Cascade Arc magmatism revealed by LA–ICP–MS U–Pb zircon dating". Canadian Journal of Earth Sciences. 55 (5): 443–462. Bibcode:2018CaJES..55..443M. doi:10.1139/cjes-2017-0167. hdl: 1807/87390 . ISSN 0008-4077.
↑ Tepper, Jeffrey H.; Kuehner, Scott M. (May 2004). "Geochemistry of Mafic Enclaves and Host Granitoids from the Chilliwack Batholith, Washington: Chemical Exchange Processes between Coexisting Mafic and Felsic Magmas and Implications for the Interpretation of Enclave Chemical Traits". The Journal of Geology. 112 (3): 349–367. Bibcode:2004JG....112..349T. doi:10.1086/382764. JSTOR 10.1086/382764. OCLC 98228216. S2CID 43130146.
↑ Dennis Martin, Feeney (2008). Timing and Nature of Post-Collapse Sedimentation in Kulshan Caldera, North Cascades, Washington (Thesis). Western Washington University. doi:10.25710/0wqt-v628. OCLC 1030748593. ZNy0YgEACAAJ at Google Books.
↑ Mullen, Emily K. (2011). Petrology and geochemistry of the Mount Baker volcanic field : constraints on source regions and terrane boundaries, and comparison with other Cascade Arc volcanic centers (Thesis). University of Washington. hdl:1773/20946. ProQuest f490cf1f3c2b316b1326e6a819b69707 Academia:75469235.
↑ James, Eric William (1980). Geology and Petrology of the Lake Ann Stock and Associated Rocks (Thesis). Western Washington University. doi:10.25710/r3dp-d443. OL 13589973M.
↑ "Geology and History Summary for Mount Baker". U.S. Geological Survey .
1 2 Hildreth, Wes (1996). "Kulshan caldera: A Quaternary subglacial caldera in the North Cascades, Washington". Geological Society of America Bulletin. 108 (7): 786–793. Bibcode:1996GSAB..108..786H. doi:10.1130/0016-7606(1996)108<0786:kcaqsc>2.3.co;2. S2CID 129795941. USGS 70018518.
↑ Hildreth, Wes (2003). "Supplemental material: Eruptive history and geochronology of the Mount Baker volcanic field, Washington". Geological Society of America Bulletin. 115 (6): 729–764. doi: 10.1130/2003091 . In Hildreth, Wes; Fierstein, Judy; Lanphere, Marvin (2003). "Eruptive history and geochronology of the Mount Baker volcanic field, Washington". Geological Society of America Bulletin. 115 (6): 729–764. Bibcode:2003GSAB..115..729H. doi:10.1130/0016-7606(2003)115<0729:EHAGOT>2.0.CO;2. S2CID 140538576. USGS 70025620 ResearchGate:249526873.
↑ Wells, Ray E.; McCaffrey, Robert (2013). "Steady rotation of the Cascade arc". Geology. 41 (9): 1027–1030. Bibcode:2013Geo....41.1027W. doi: 10.1130/G34514.1 . S2CID 129510320. ResearchGate:256082766 USGS 70117449.
↑ Poland, Michael P.; Lisowski, Michael; Dzurisin, Daniel; Kramer, Rebecca; McLay, Megan; Pauk, Ben (2017). "Volcano geodesy in the Cascade arc, USA". Bulletin of Volcanology. 79 (8): 59. Bibcode:2017BVol...79...59P. doi:10.1007/s00445-017-1140-x. S2CID 133965157.
↑ "Geology and History Summary for Mount Mazama and Crater Lake". U.S. Geological Survey .
↑ Bacon, Charles R. (1983). "Eruptive history of Mount Mazama and Crater Lake Caldera, Cascade Range, U.S.A." Journal of Volcanology and Geothermal Research. 18 (1): 57–115. Bibcode:1983JVGR...18...57B. doi:10.1016/0377-0273(83)90004-5.
↑ Clynne, Michael A. (1990). "Stratigraphic, lithologic and major element geochemical constraints on magmatic evolution at Lassen volcanic center, California". Journal of Geophysical Research. 95 (B12): 19651–19669. Bibcode:1990JGR....9519651C. doi:10.1029/JB095iB12p19651.
↑ Lanphere, M. A.; Champion, D. E.; Clynne, M. A.; Lowenstern, J. B.; Sarna-Wojcicki, A. M.; Wooden, J. L. (2004). "Age of the Rockland tephra, western USA". Quaternary Research. 62 (1): 94–104. Bibcode:2004QuRes..62...94L. doi:10.1016/j.yqres.2004.03.001. S2CID 140689415.
↑ Berman, Robert G.; Armstrong, Richard Lee (1980). "Geology of the Coquihalla Volcanic Complex, southwestern British Columbia". Canadian Journal of Earth Sciences. 17 (8): 985–995. doi:10.1139/e80-099. S2CID 129826748.
↑ Swanson, Donald A.; Haugerud, Ralph Albert, eds. (1994). "Hammond, Paul E., Brunstad, Keith A., and King, John F. Mid-Tertiary volcanism east of Mount Rainier: Fifes Peak volcano-caldera and Bumping Lake pluton- Mount Aix caldera". Geologic Field Trips in the Pacific Northwest. Department of Geological Sciences, University of Washington; Annual Meeting of the Geological Society of America, Seattle, Washington, October 24-27, 1994. OCLC 35377547.
↑ King, John Frederick (1994). Magmatic Evolution and Eruptive History of the Granitic Bumping Lake Pluton, Washington: Source of the Bumping River and Cash Prairie Tuffs (Thesis). Portland State University. doi: 10.15760/etd.6649 . S2CID 134176687.