Drew Downs in Iceland with a glacier in hte background.
Drew T. Downs
I am a research geologist with the Hawaiian Volcano Observatory and my main areas of research revolve around constructing geologic maps and unraveling the eruptive histories of volcanoes. To do this, I use a multidisciplinary approach using field studies, physical volcanology, geochronology, geochemistry, petrology, remote sensing, and many more techniques.
I have worked on volcanoes and volcanic fields in a variety of settings, including subduction-related arc volcanoes within New Zealand and the southern Cascades of California, the monogenetic volcanic field of of Harrat Rahat in Saudi Arabia, and unraveling the eruptive history and processes of volcanic rocks of the Hawaiian Islands.
Throughout my research career I have participated in studies on explosive and effusive volcanism ranging from high-silica rhyolites and trachytes to basaltic lava flows. Unraveling the eruptive history preserved at the surface to understanding deeper volcanic processes has led me to use a wide variety of techniques, such as field studies, physical volcanology, geochronology, geochemistry, petrology, paleomagnetism, remote sensing, and other novel methods that help to understand volcanic processes and further understanding of their hazards.
Education and Certifications
2014 - Ph.D., Geology, University of Auckland (New Zealand)
2009 - MSc, Southern Illinois University
2007 - BSc, Southern Illinois University
Science and Products
Vesicularity, grain size, and grain shape of basaltic pyroclasts from Kīlauea and Mauna Loa volcanoes, Island of Hawaiʻi
This dataset includes sample information, vesicularity by pycnometer, grain size and shape data by CAMSIZER, and measurements of crushed and thin section mounted grains by microscope. All studied samples were from scoria and air-fall-tephra deposits (most formed in Hawaiian lava fountains) collected around the summits of Mauna Loa and Kīlauea volcanoes, Island of Hawaiʻi. These data were used to d
Major- and trace-element chemical analyses of whole-rock and glass from the Kamakaiʻa Hills of the Southwest Rift Zone of Kīlauea volcano, Hawaiʻi
This dataset includes wavelength dispersive X-ray fluorescence (WD-XRF) major-oxide and trace-element whole-rock analyses, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) trace-element whole-rock analyses, and glass analyses by electron microprobe of scoria and lava samples from the Kamakaiʻa Hills of the Southwest Rift Zone of Kīlauea volcano, Island of Hawaiʻi. Whole-rock
Colorimeter data for the summit water lake at Kīlauea Volcano, Island of Hawaiʻi, 2020
In 2018, a large effusive eruption on the lower flank of Kīlauea Volcano was associated with collapse and subsidence of the summit caldera floor (Neal and others, 2019). The bottom of Halemaʻumaʻu, a crater nested within the summit caldera, subsided by more than 500 m. In July 2019, water was observed ponding on the deepest part of the Halemaʻumaʻu crater floor and the water rose and enlarged in
Sample details and near-real-time ED-XRF, grain size, and grain shape data collected during the November – December 2022 eruption of Mauna Loa volcano, Island of Hawaiʻi
At 11:21 p.m. (Hawaii Standard Time [HST]) on November 27, 2022, Mauna Loa volcano on the Island of Hawaiʻi started erupting from fissures at its summit caldera, Mokuʻāweoweo. This was followed shortly afterwards by the opening of a segment of fissures in the direction of the Southwest Rift Zone. These were mostly within the structural boundary of the caldera, so their location is denoted as ‘Sout
Electron microprobe data for plagioclase, olivine, pyroxene, and spinel in volcanic rocks from the Matan volcanic center located within the Harrat Rahat volcanic field, Kingdom of Saudi Arabia
Mineral compositions are reported for Quaternary volcanic rocks of the Matan volcanic center, northern Harrat Rahat, Saudi Arabia. Compositions were measured by wavelength-dispersive methods with the 5-spectrometer JEOL-8900 electron microprobe at the USGS facility in Menlo Park, California; background-corrected X-ray intensities were reduced to oxide weight concentrations with the JEOL proprietar
Water-level data for the crater lake at the summit of Kilauea Volcano, Island of Hawai'i, 2019-2020
During 2018, Kilauea Volcano, on the Island of Hawaiii, had a large effusive eruption (~1 cubic kilometer of lava) on the lower East Rift Zone that caused widespread destruction (Neal and others, 2019; Dietterich and others, 2021). This lower flank eruption was accompanied by one of the largest collapses of the summit caldera in two hundred years, with portions of the caldera floor subsiding more
Database for the geologic map of the Paeroa Fault block and surrounding area, Taupo Volcanic Zone, New Zealand
The Taupo Volcanic Zone (TVZ), New Zealand, is the most productive area of explosive silicic volcanism in the world. Faulted early and middle Pleistocene volcanic products are generally concealed beneath voluminous, generally unfaulted, younger volcanic products. An exception is the southeast margin of the TVZ where the two parallel, northeast-trending Paeroa and Te Weta Fault blocks expose Quater
Database for the Geologic Map of the Northern Harrat Rahat Volcanic Field, Kingdom of Saudi Arabia
The Harrat Rahat volcanic field, located in the west-central part of the Kingdom of Saudi Arabia, is the largest of 15 harrats (Arabic for 'volcanic field') hosted within the Arabian plate. Harrat Rahat is 50 to 75 km wide (east-west) and 300 km long (north-south), covering an area of approximately 20,000 square kilometers and encompassing more than 900 observable vents. The overall map area and i
Geologic map of the northern Harrat Rahat volcanic field, Kingdom of Saudi Arabia
Harrat Rahat, in the west-central part of the Kingdom of Saudi Arabia, is the largest of 15 Cenozoic harrats (Arabic for “volcanic field”) distributed on the Arabian plate. It extends more than 300 km north-south and 50 to 75 km east-west, and it covers an area of approximately 20,000 km2, has a volume of approximately 2,000 km3, and encompasses more than 900 observable vents. Volcanism commenced
Drew Downs in Iceland
Drew Downs in Iceland with a glacier in hte background.
Filter Total Items: 20
Tracking magma pathways and surface faulting in the Southwest Rift Zone and the Koaʻe fault system (Kīlauea volcano, Hawai ‘i) using photogrammetry and structural observations
Volcanic islands are often subject to flank instability, resulting from a combination of magmatic intrusions along rift zones and gravitational spreading causing extensional faulting at the surface. Here, we study the Koaʻe fault system (KFS), located south of the summit caldera of Kīlauea volcano in Hawaiʻi, one of the most active volcanoes on Earth, prone to active faulting, episodic dike intrus
Authors
Stefano Mannini, Joël Ruch, Richard W. Hazlett, Drew T. Downs, Carolyn Parcheta, Steven P. Lundblad, James Anderson, Ryan L. Perroy, Nicolas Oestreicher
Overview of the Cenozoic geology of the northern Harrat Rahat volcanic field, Kingdom of Saudi Arabia
The Harrat Rahat volcanic field, located in the west-central part of the Kingdom of Saudi Arabia, is one of the larger Cenozoic harrats among the more than 17 harrats situated upon the Arabia Plate. The map plate contained herein shows, at a scale of 1:100,000, the mapped volcanic geology of northern Harrat Rahat, which consists of the northernmost one-fifth of Harrat Rahat. Northern Harrat Rahat
Authors
Joel E. Robinson, Drew T. Downs
Eruptive history within the vicinity of Al Madīnah in northern Harrat Rahat, Kingdom of Saudi Arabia
The northernmost part of the Harrat Rahat volcanic field contains early Pleistocene to Holocene mafic eruptive products within the vicinity of the city of Al Madīnah, Kingdom of Saudi Arabia. A detailed geologic investigation into the eruptive history of a 570 square kilometer (km2) area covering Al Madīnah and the surrounding area has yielded 33 mapped Quaternary volcanic units consisting of lava
Authors
Drew T. Downs, Mark E. Stelten, Duane E. Champion, Hannah R. Dietterich, Khalid Hassan, Jamal Shawali
Eruptive history of northern Harrat Rahat—Volume, timing, and composition of volcanism over the past 1.2 million years
Harrat Rahat, one of several large, basalt-dominated volcanic fields in the western part of the Kingdom of Saudi Arabia, is a prime example of continental, intraplate volcanism. Excellent exposure makes this an outstanding site to investigate changing volcanic flux and composition through time. We present 93 40Ar/39Ar ages and 6 36Cl surface-exposure ages for volcanic deposits throughout northern
Authors
Mark E. Stelten, Drew T. Downs, Duane E. Champion, Hannah R. Dietterich, Andrew T. Calvert, Thomas W. Sisson, Gail A. Mahood, Hani M. Zahran
Lava flow emplacement in Harrat Rahat with implications for eruptions in mafic volcanic fields
Mafic volcanic fields are widespread, but few have erupted in historical times, providing limited observations of the magnitudes, dynamics, and timescales of lava flow emplacement in these settings. The Harrat Rahat volcanic field in western Saudi Arabia offers a good opportunity to study eruptions in such a setting, with a historical eruption in 1256 C.E. (654 in the year of the Hijra) and numero
Authors
Hannah R. Dietterich, Drew T. Downs, Mark E. Stelten
The duration and characteristics of magmatic differentiation from basalt to trachyte within the Matan volcanic center, northern Harrat Rahat, Kingdom of Saudi Arabia
A fundamental goal of igneous petrology is to quantify the durations required to produce evolved magmas following influx of basalt into the crust. However, in many cases, complex field relations and (or) the presence of a long-lived magmatic system make it difficult to assess how basaltic inputs relate to more evolved magmas, therefore precluding calculation of meaningful timescales. Here we prese
Authors
Mark E. Stelten, Drew T. Downs, Hannah R. Dietterich, Gail A. Mahood, Andrew T. Calvert, Thomas W. Sisson, Molly R. Witter, Hani M. Zahran, Jamal Shawali
Explosive trachyte eruptions from the Al Efairia volcanic center in northern Harrat Rahat, Kingdom of Saudi Arabia
Harrat Rahat is an alkali basalt, continental, intraplate volcanic field located within the central-western part of the Kingdom of Saudi Arabia. The northern quarter of Harrat Rahat contains evolved volcanic products that achieve trachyte compositions (>60 weight percent SiO2). Within the Al Efairia volcanic center, pyroclastic-flow and -surge deposits that reflect explosive trachyte volcanism (an
Authors
Drew T. Downs, Mark E. Stelten, Hannah R. Dietterich, Duane E. Champion, Gail A. Mahood, Thomas W. Sisson, Andrew T. Calvert, Jamal Shawali
Paleomagnetism of the Harrat Rahat volcanic field, Kingdom of Saudi Arabia—Geologic unit correlations and geomagnetic cryptochron identifications
Paleomagnetic rock samples were collected from 173 drill sites in the Quaternary alkali basaltic volcanic field of northern Harrat Rahat, Kingdom of Saudi Arabia. Laboratory measurements on these samples established that lava flows and vent complexes—identified and mapped from field characteristics, rock types, and compositions as products of single or temporally close eruptions—typically record s
Authors
Duane E. Champion, Drew T. Downs, Mark E. Stelten, Joel E. Robinson, Thomas W. Sisson, Jamal Shawali, Khalid Hassan, Hani M. Zahran
Mantle origin and crustal differentiation of basalts and hawaiites of northern Harrat Rahat, Kingdom of Saudi Arabia
Quaternary volcanic rocks of northern Harrat Rahat, Kingdom of Saudi Arabia, are chiefly alkali basalts with subordinate transitional basalts, hawaiites, mugearites, benmoreites, and trachytes. Geochemical and isotopic results indicate that crystallization-differentiation, mixing, and cumulate reassimilation within the magmatic system produced most of its compositional diversity, with only minor i
Authors
Thomas W. Sisson, Drew T. Downs, Andrew T. Calvert, Hannah R. Dietterich, Gail A. Mahood, Vincent J.M. Salters, Mark E. Stelten, Jamal Shawali
Isotopic and geochemical evidence for the source of volcanism at Harrat Rahat, Kingdom of Saudi Arabia
Pleistocene and Holocene basalts, hawaiites, mugearites, benmoreites, and trachytes from the northern part of the Harrat Rahat volcanic field, Kingdom of Saudi Arabia, were analyzed for Sr, Nd, Hf, and Pb isotopic compositions. Evolved trachytes with Mg number <0.1 (Mg# = Mg/[Mg+Fe2+], molar) have relatively radiogenic Sr isotopic compositions indicating that they were influenced by contamination
Authors
Vincent J.M. Salters, Afi Sachi-Kocher, Drew T. Downs, Mark E. Stelten, Thomas W. Sisson
Chemistry and petrography of early 19th century basaltic andesites and basalts from the Kamakaiʻa Hills in the Southwest Rift Zone of Kīlauea volcano, Hawaiʻi
Kīlauea is a frequently active, open-system volcano on the Island of Hawaiʻi known for erupting olivine-dominated tholeiitic basalt compositions. On rare occasions it erupts more differentiated magmas (<1% of erupted volume), such as basaltic andesites and andesites, from its rift zones. These differentiated magmas offer an opportunity to understand better the petrology, magma storage, magma mixin
Authors
Drew T. Downs, May Sas, Richard W. Hazlett
A multidisciplinary investigation into the eruptive style, processes, and duration of a Cascades back-arc tholeiitic basalt: A case study of the Brushy Butte flow field, northern California, United States
The Cascades back-arc in northern California is dominated by monogenetic tholeiitic basalts that erupted throughout the Pleistocene. Elucidating their eruptive history and processes is important for understanding potential future eruptions here. We focus on the well-exposed monogenetic volcano that emplaced the Brushy Butte flow field, which constructed a ∼150 m tall edifice, has flow lobes up to
Authors
Drew T. Downs, Duane E. Champion, Michael A. Clynne, L. J. Patrick Muffler
Non-USGS Publications**
Downs, D.T., Rowland, J.V., Wilson, C.J.N., Rosenberg, M.D., Leonard, G.S., and Calvert, A.T., 2014, Evolution of the intra-arc Taupo-Reporoa Basin within the Taupo Volcanic Zone of New Zealand: Geopshere, v. 10, p. 185-206, doi:10.1130/GES00965.1.
Downs, D.T., Wilson, C.J.N., Cole, J.W., Rowland, J.V., Calvert, A.T., Leonard, G.S., and Keall, J.M., 2014, Age and eruptive center of the Paeroa Subgroup ignimbrites (Whakamaru Group) within the Taupo Volcanic Zone of New Zealand: Geological Society of America Bulletin, v. 126, p. 1131-1144, doi:10.1130/B30891.1.
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
Science and Products
- Data
Vesicularity, grain size, and grain shape of basaltic pyroclasts from Kīlauea and Mauna Loa volcanoes, Island of Hawaiʻi
This dataset includes sample information, vesicularity by pycnometer, grain size and shape data by CAMSIZER, and measurements of crushed and thin section mounted grains by microscope. All studied samples were from scoria and air-fall-tephra deposits (most formed in Hawaiian lava fountains) collected around the summits of Mauna Loa and Kīlauea volcanoes, Island of Hawaiʻi. These data were used to dMajor- and trace-element chemical analyses of whole-rock and glass from the Kamakaiʻa Hills of the Southwest Rift Zone of Kīlauea volcano, Hawaiʻi
This dataset includes wavelength dispersive X-ray fluorescence (WD-XRF) major-oxide and trace-element whole-rock analyses, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) trace-element whole-rock analyses, and glass analyses by electron microprobe of scoria and lava samples from the Kamakaiʻa Hills of the Southwest Rift Zone of Kīlauea volcano, Island of Hawaiʻi. Whole-rockColorimeter data for the summit water lake at Kīlauea Volcano, Island of Hawaiʻi, 2020
In 2018, a large effusive eruption on the lower flank of Kīlauea Volcano was associated with collapse and subsidence of the summit caldera floor (Neal and others, 2019). The bottom of Halemaʻumaʻu, a crater nested within the summit caldera, subsided by more than 500 m. In July 2019, water was observed ponding on the deepest part of the Halemaʻumaʻu crater floor and the water rose and enlarged inSample details and near-real-time ED-XRF, grain size, and grain shape data collected during the November – December 2022 eruption of Mauna Loa volcano, Island of Hawaiʻi
At 11:21 p.m. (Hawaii Standard Time [HST]) on November 27, 2022, Mauna Loa volcano on the Island of Hawaiʻi started erupting from fissures at its summit caldera, Mokuʻāweoweo. This was followed shortly afterwards by the opening of a segment of fissures in the direction of the Southwest Rift Zone. These were mostly within the structural boundary of the caldera, so their location is denoted as ‘SoutElectron microprobe data for plagioclase, olivine, pyroxene, and spinel in volcanic rocks from the Matan volcanic center located within the Harrat Rahat volcanic field, Kingdom of Saudi Arabia
Mineral compositions are reported for Quaternary volcanic rocks of the Matan volcanic center, northern Harrat Rahat, Saudi Arabia. Compositions were measured by wavelength-dispersive methods with the 5-spectrometer JEOL-8900 electron microprobe at the USGS facility in Menlo Park, California; background-corrected X-ray intensities were reduced to oxide weight concentrations with the JEOL proprietarWater-level data for the crater lake at the summit of Kilauea Volcano, Island of Hawai'i, 2019-2020
During 2018, Kilauea Volcano, on the Island of Hawaiii, had a large effusive eruption (~1 cubic kilometer of lava) on the lower East Rift Zone that caused widespread destruction (Neal and others, 2019; Dietterich and others, 2021). This lower flank eruption was accompanied by one of the largest collapses of the summit caldera in two hundred years, with portions of the caldera floor subsiding moreDatabase for the geologic map of the Paeroa Fault block and surrounding area, Taupo Volcanic Zone, New Zealand
The Taupo Volcanic Zone (TVZ), New Zealand, is the most productive area of explosive silicic volcanism in the world. Faulted early and middle Pleistocene volcanic products are generally concealed beneath voluminous, generally unfaulted, younger volcanic products. An exception is the southeast margin of the TVZ where the two parallel, northeast-trending Paeroa and Te Weta Fault blocks expose QuaterDatabase for the Geologic Map of the Northern Harrat Rahat Volcanic Field, Kingdom of Saudi Arabia
The Harrat Rahat volcanic field, located in the west-central part of the Kingdom of Saudi Arabia, is the largest of 15 harrats (Arabic for 'volcanic field') hosted within the Arabian plate. Harrat Rahat is 50 to 75 km wide (east-west) and 300 km long (north-south), covering an area of approximately 20,000 square kilometers and encompassing more than 900 observable vents. The overall map area and i - Maps
Geologic map of the northern Harrat Rahat volcanic field, Kingdom of Saudi Arabia
Harrat Rahat, in the west-central part of the Kingdom of Saudi Arabia, is the largest of 15 Cenozoic harrats (Arabic for “volcanic field”) distributed on the Arabian plate. It extends more than 300 km north-south and 50 to 75 km east-west, and it covers an area of approximately 20,000 km2, has a volume of approximately 2,000 km3, and encompasses more than 900 observable vents. Volcanism commenced - Multimedia
Drew Downs in Iceland
Drew Downs in Iceland with a glacier in hte background.
Drew Downs in Iceland with a glacier in hte background.
- Publications
Filter Total Items: 20
Tracking magma pathways and surface faulting in the Southwest Rift Zone and the Koaʻe fault system (Kīlauea volcano, Hawai ‘i) using photogrammetry and structural observations
Volcanic islands are often subject to flank instability, resulting from a combination of magmatic intrusions along rift zones and gravitational spreading causing extensional faulting at the surface. Here, we study the Koaʻe fault system (KFS), located south of the summit caldera of Kīlauea volcano in Hawaiʻi, one of the most active volcanoes on Earth, prone to active faulting, episodic dike intrusAuthorsStefano Mannini, Joël Ruch, Richard W. Hazlett, Drew T. Downs, Carolyn Parcheta, Steven P. Lundblad, James Anderson, Ryan L. Perroy, Nicolas OestreicherOverview of the Cenozoic geology of the northern Harrat Rahat volcanic field, Kingdom of Saudi Arabia
The Harrat Rahat volcanic field, located in the west-central part of the Kingdom of Saudi Arabia, is one of the larger Cenozoic harrats among the more than 17 harrats situated upon the Arabia Plate. The map plate contained herein shows, at a scale of 1:100,000, the mapped volcanic geology of northern Harrat Rahat, which consists of the northernmost one-fifth of Harrat Rahat. Northern Harrat Rahat
AuthorsJoel E. Robinson, Drew T. DownsEruptive history within the vicinity of Al Madīnah in northern Harrat Rahat, Kingdom of Saudi Arabia
The northernmost part of the Harrat Rahat volcanic field contains early Pleistocene to Holocene mafic eruptive products within the vicinity of the city of Al Madīnah, Kingdom of Saudi Arabia. A detailed geologic investigation into the eruptive history of a 570 square kilometer (km2) area covering Al Madīnah and the surrounding area has yielded 33 mapped Quaternary volcanic units consisting of lavaAuthorsDrew T. Downs, Mark E. Stelten, Duane E. Champion, Hannah R. Dietterich, Khalid Hassan, Jamal ShawaliEruptive history of northern Harrat Rahat—Volume, timing, and composition of volcanism over the past 1.2 million years
Harrat Rahat, one of several large, basalt-dominated volcanic fields in the western part of the Kingdom of Saudi Arabia, is a prime example of continental, intraplate volcanism. Excellent exposure makes this an outstanding site to investigate changing volcanic flux and composition through time. We present 93 40Ar/39Ar ages and 6 36Cl surface-exposure ages for volcanic deposits throughout northernAuthorsMark E. Stelten, Drew T. Downs, Duane E. Champion, Hannah R. Dietterich, Andrew T. Calvert, Thomas W. Sisson, Gail A. Mahood, Hani M. ZahranLava flow emplacement in Harrat Rahat with implications for eruptions in mafic volcanic fields
Mafic volcanic fields are widespread, but few have erupted in historical times, providing limited observations of the magnitudes, dynamics, and timescales of lava flow emplacement in these settings. The Harrat Rahat volcanic field in western Saudi Arabia offers a good opportunity to study eruptions in such a setting, with a historical eruption in 1256 C.E. (654 in the year of the Hijra) and numeroAuthorsHannah R. Dietterich, Drew T. Downs, Mark E. SteltenThe duration and characteristics of magmatic differentiation from basalt to trachyte within the Matan volcanic center, northern Harrat Rahat, Kingdom of Saudi Arabia
A fundamental goal of igneous petrology is to quantify the durations required to produce evolved magmas following influx of basalt into the crust. However, in many cases, complex field relations and (or) the presence of a long-lived magmatic system make it difficult to assess how basaltic inputs relate to more evolved magmas, therefore precluding calculation of meaningful timescales. Here we preseAuthorsMark E. Stelten, Drew T. Downs, Hannah R. Dietterich, Gail A. Mahood, Andrew T. Calvert, Thomas W. Sisson, Molly R. Witter, Hani M. Zahran, Jamal ShawaliExplosive trachyte eruptions from the Al Efairia volcanic center in northern Harrat Rahat, Kingdom of Saudi Arabia
Harrat Rahat is an alkali basalt, continental, intraplate volcanic field located within the central-western part of the Kingdom of Saudi Arabia. The northern quarter of Harrat Rahat contains evolved volcanic products that achieve trachyte compositions (>60 weight percent SiO2). Within the Al Efairia volcanic center, pyroclastic-flow and -surge deposits that reflect explosive trachyte volcanism (anAuthorsDrew T. Downs, Mark E. Stelten, Hannah R. Dietterich, Duane E. Champion, Gail A. Mahood, Thomas W. Sisson, Andrew T. Calvert, Jamal ShawaliPaleomagnetism of the Harrat Rahat volcanic field, Kingdom of Saudi Arabia—Geologic unit correlations and geomagnetic cryptochron identifications
Paleomagnetic rock samples were collected from 173 drill sites in the Quaternary alkali basaltic volcanic field of northern Harrat Rahat, Kingdom of Saudi Arabia. Laboratory measurements on these samples established that lava flows and vent complexes—identified and mapped from field characteristics, rock types, and compositions as products of single or temporally close eruptions—typically record sAuthorsDuane E. Champion, Drew T. Downs, Mark E. Stelten, Joel E. Robinson, Thomas W. Sisson, Jamal Shawali, Khalid Hassan, Hani M. ZahranMantle origin and crustal differentiation of basalts and hawaiites of northern Harrat Rahat, Kingdom of Saudi Arabia
Quaternary volcanic rocks of northern Harrat Rahat, Kingdom of Saudi Arabia, are chiefly alkali basalts with subordinate transitional basalts, hawaiites, mugearites, benmoreites, and trachytes. Geochemical and isotopic results indicate that crystallization-differentiation, mixing, and cumulate reassimilation within the magmatic system produced most of its compositional diversity, with only minor iAuthorsThomas W. Sisson, Drew T. Downs, Andrew T. Calvert, Hannah R. Dietterich, Gail A. Mahood, Vincent J.M. Salters, Mark E. Stelten, Jamal ShawaliIsotopic and geochemical evidence for the source of volcanism at Harrat Rahat, Kingdom of Saudi Arabia
Pleistocene and Holocene basalts, hawaiites, mugearites, benmoreites, and trachytes from the northern part of the Harrat Rahat volcanic field, Kingdom of Saudi Arabia, were analyzed for Sr, Nd, Hf, and Pb isotopic compositions. Evolved trachytes with Mg number <0.1 (Mg# = Mg/[Mg+Fe2+], molar) have relatively radiogenic Sr isotopic compositions indicating that they were influenced by contaminationAuthorsVincent J.M. Salters, Afi Sachi-Kocher, Drew T. Downs, Mark E. Stelten, Thomas W. SissonChemistry and petrography of early 19th century basaltic andesites and basalts from the Kamakaiʻa Hills in the Southwest Rift Zone of Kīlauea volcano, Hawaiʻi
Kīlauea is a frequently active, open-system volcano on the Island of Hawaiʻi known for erupting olivine-dominated tholeiitic basalt compositions. On rare occasions it erupts more differentiated magmas (<1% of erupted volume), such as basaltic andesites and andesites, from its rift zones. These differentiated magmas offer an opportunity to understand better the petrology, magma storage, magma mixinAuthorsDrew T. Downs, May Sas, Richard W. HazlettA multidisciplinary investigation into the eruptive style, processes, and duration of a Cascades back-arc tholeiitic basalt: A case study of the Brushy Butte flow field, northern California, United States
The Cascades back-arc in northern California is dominated by monogenetic tholeiitic basalts that erupted throughout the Pleistocene. Elucidating their eruptive history and processes is important for understanding potential future eruptions here. We focus on the well-exposed monogenetic volcano that emplaced the Brushy Butte flow field, which constructed a ∼150 m tall edifice, has flow lobes up toAuthorsDrew T. Downs, Duane E. Champion, Michael A. Clynne, L. J. Patrick MufflerNon-USGS Publications**
Downs, D.T., Rowland, J.V., Wilson, C.J.N., Rosenberg, M.D., Leonard, G.S., and Calvert, A.T., 2014, Evolution of the intra-arc Taupo-Reporoa Basin within the Taupo Volcanic Zone of New Zealand: Geopshere, v. 10, p. 185-206, doi:10.1130/GES00965.1.Downs, D.T., Wilson, C.J.N., Cole, J.W., Rowland, J.V., Calvert, A.T., Leonard, G.S., and Keall, J.M., 2014, Age and eruptive center of the Paeroa Subgroup ignimbrites (Whakamaru Group) within the Taupo Volcanic Zone of New Zealand: Geological Society of America Bulletin, v. 126, p. 1131-1144, doi:10.1130/B30891.1.**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.