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Cracked Mountain (CM) is a basaltic volcano within the northern extension of the Cascade volcanic arc into southwest, British Columbia, Canada (i.e. Garibaldi Volcanic Belt) and is dated at 401 ± 38 ka (40Ar/39Ar). The edifice covers an area of ~1.5 km2 and has a volume of 0.18 km3. The volcano features steep margins with local relief of ~250 m (1,650 m a.s.l), is dissected by abundant 0.5 to ~20 m wide extensional cracks with depths up to 30 m, and has a highly eroded top. The edifice is dominated by massive to poorly stratified, moderately to pervasively palagonitized lapilli tuffs, comprising vitric fine ash to lapilli. Juvenile pyroclasts have blocky to highly vesiculated shapes consistent with a phreatomagmatic (i.e. explosive) origin. The lapilli tuffs are intruded by and mingled with coherent to disaggregated lobes of peperitic pillowed lavas. Contacts between lapilli tuff and peperitic pillowed lava show soft-sediment deformation and in-situ quench-fragmentation indicating that the tephra was both unconsolidated and water-saturated at the time of intrusion. Local stacks of pillow lava are found on the margins of the edifice. More than fifty, 0.5 to 3 m wide dykes intrude CM stratigraphy and display, either, peperitic pillowed margins or sharp, chilled margins and columnar-jointing. Measurements of paleomagnetic directions (9 sites) were made for all CM lithofacies and record a single-pole direction indicating a single monogenetic eruption. A glaciovolcanic origin is strongly suggested by the abundant subaqueous lithofacies (i.e. palagonitized tephra, pillows, peperites) and the physiographic setting of the edifice which is well above any drainage that could sustain a standing body of water. The elevation of CM and depth of surrounding valleys indicate syn-eruptive confinement by a paleo-ice sheet that was ≥850 m thick. The edifice shape, size, and surround- ing topography suggest a ‘leaky’ paleolake system capable of supporting ~0.36 km3 of water. The glacio

Cracked Mountain (CM) is a basaltic volcano within the northern extension of the Cascade volcanic arc into southwest, British Columbia, Canada (i.e. Garibaldi Volcanic Belt) and is dated at 401 ± 38 ka (40Ar/39Ar). The edifice covers an area of ~1.5 km2 and has a volume of 0.18 km3. The volcano features steep margins with local relief of ~250 m (1,650 m a.s.l), is dissected by abundant 0.5 to ~20 m wide extensional cracks with depths up to 30 m, and has a highly eroded top. The edifice is dominated by massive to poorly stratified, moderately to pervasively palagonitized lapilli tuffs, comprising vitric fine ash to lapilli. Juvenile pyroclasts have blocky to highly vesiculated shapes consistent with a phreatomagmatic (i.e. explosive) origin. The lapilli tuffs are intruded by and mingled with coherent to disaggregated lobes of peperitic pillowed lavas. Contacts between lapilli tuff and peperitic pillowed lava show soft-sediment deformation and in-situ quench-fragmentation indicating that the tephra was both unconsolidated and water-saturated at the time of intrusion. Local stacks of pillow lava are found on the margins of the edifice. More than fifty, 0.5 to 3 m wide dykes intrude CM stratigraphy and display, either, peperitic pillowed margins or sharp, chilled margins and columnar-jointing. Measurements of paleomagnetic directions (9 sites) were made for all CM lithofacies and record a single-pole direction indicating a single monogenetic eruption. A glaciovolcanic origin is strongly suggested by the abundant subaqueous lithofacies (i.e. palagonitized tephra, pillows, peperites) and the physiographic setting of the edifice which is well above any drainage that could sustain a standing body of water. The elevation of CM and depth of surrounding valleys indicate syn-eruptive confinement by a paleo-ice sheet that was ≥850 m thick. The edifice shape, size, and surround- ing topography suggest a ‘leaky’ paleolake system capable of supporting ~0.36 km3 of water. The glacio

Cracked Mountain (CM) is a basaltic volcano within the northern extension of the Cascade volcanic arc into southwest, British Columbia, Canada (i.e. Garibaldi Volcanic Belt) and is dated at 401 ± 38 ka (40Ar/39Ar). The edifice covers an area of ~1.5 km2 and has a volume of 0.18 km3. The volcano features steep margins with local relief of ~250 m (1,650 m a.s.l), is dissected by abundant 0.5 to ~20 m wide extensional cracks with depths up to 30 m, and has a highly eroded top. The edifice is dominated by massive to poorly stratified, moderately to pervasively palagonitized lapilli tuffs, comprising vitric fine ash to lapilli. Juvenile pyroclasts have blocky to highly vesiculated shapes consistent with a phreatomagmatic (i.e. explosive) origin. The lapilli tuffs are intruded by and mingled with coherent to disaggregated lobes of peperitic pillowed lavas. Contacts between lapilli tuff and peperitic pillowed lava show soft-sediment deformation and in-situ quench-fragmentation indicating that the tephra was both unconsolidated and water-saturated at the time of intrusion. Local stacks of pillow lava are found on the margins of the edifice. More than fifty, 0.5 to 3 m wide dykes intrude CM stratigraphy and display, either, peperitic pillowed margins or sharp, chilled margins and columnar-jointing. Measurements of paleomagnetic directions (9 sites) were made for all CM lithofacies and record a single-pole direction indicating a single monogenetic eruption. A glaciovolcanic origin is strongly suggested by the abundant subaqueous lithofacies (i.e. palagonitized tephra, pillows, peperites) and the physiographic setting of the edifice which is well above any drainage that could sustain a standing body of water. The elevation of CM and depth of surrounding valleys indicate syn-eruptive confinement by a paleo-ice sheet that was ≥850 m thick. The edifice shape, size, and surround- ing topography suggest a ‘leaky’ paleolake system capable of supporting ~0.36 km3 of water. The glacio

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hudak, M. R., Bindeman, I. N., Loewen, M. W., & Giachetti, T. Syn-eruptive hydration of volcanic ash records pyroclast-water interaction in explosive eruptions. Geophysical Research Letters, 48(23), (2021): e2021GL094141, https://doi.org/10.1029/2021GL094141., Magma-water interaction can dramatically influence the explosivity of volcanic eruptions. However, syn- and post-eruptive diffusion of external (non-magmatic) water into volcanic glass remains poorly constrained and may bias interpretation of water in juvenile products. Hydrogen isotopes in ash from the 2009 eruption of Redoubt Volcano, Alaska, record syn-eruptive hydration by vaporized glacial meltwater. Both ash aggregation and hydration occurred in the wettest regions of the plume, which resulted in the removal and deposition of the most hydrated ash in proximal areas <50 km from the vent. Diffusion models show that the high temperatures of pyroclast-water interactions (>400°C) are more important than the cooling rate in facilitating hydration. These observations suggest that syn-eruptive glass hydration occurred where meltwater was entrained at high temperature, in the plume margins near the vent. Ash in the drier plume interior remained insulated from entrained meltwater until it cooled sufficiently to avoid significant hydration., This work was supported by a Geological Society of America Bruce L. "Biff" Reed Scholarship Award and NSF Grant EAR 1822977., 2022-05-15

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hudak, M. R., Bindeman, I. N., Loewen, M. W., & Giachetti, T. Syn-eruptive hydration of volcanic ash records pyroclast-water interaction in explosive eruptions. Geophysical Research Letters, 48(23), (2021): e2021GL094141, https://doi.org/10.1029/2021GL094141., Magma-water interaction can dramatically influence the explosivity of volcanic eruptions. However, syn- and post-eruptive diffusion of external (non-magmatic) water into volcanic glass remains poorly constrained and may bias interpretation of water in juvenile products. Hydrogen isotopes in ash from the 2009 eruption of Redoubt Volcano, Alaska, record syn-eruptive hydration by vaporized glacial meltwater. Both ash aggregation and hydration occurred in the wettest regions of the plume, which resulted in the removal and deposition of the most hydrated ash in proximal areas <50 km from the vent. Diffusion models show that the high temperatures of pyroclast-water interactions (>400°C) are more important than the cooling rate in facilitating hydration. These observations suggest that syn-eruptive glass hydration occurred where meltwater was entrained at high temperature, in the plume margins near the vent. Ash in the drier plume interior remained insulated from entrained meltwater until it cooled sufficiently to avoid significant hydration., This work was supported by a Geological Society of America Bruce L. "Biff" Reed Scholarship Award and NSF Grant EAR 1822977., 2022-05-15

Cracked Mountain (CM) is a basaltic volcano within the northern extension of the Cascade volcanic arc into southwest, British Columbia, Canada (i.e. Garibaldi Volcanic Belt) and is dated at 401 ± 38 ka (40Ar/39Ar). The edifice covers an area of ~1.5 km2 and has a volume of 0.18 km3. The volcano features steep margins with local relief of ~250 m (1,650 m a.s.l), is dissected by abundant 0.5 to ~20 m wide extensional cracks with depths up to 30 m, and has a highly eroded top. The edifice is dominated by massive to poorly stratified, moderately to pervasively palagonitized lapilli tuffs, comprising vitric fine ash to lapilli. Juvenile pyroclasts have blocky to highly vesiculated shapes consistent with a phreatomagmatic (i.e. explosive) origin. The lapilli tuffs are intruded by and mingled with coherent to disaggregated lobes of peperitic pillowed lavas. Contacts between lapilli tuff and peperitic pillowed lava show soft-sediment deformation and in-situ quench-fragmentation indicating that the tephra was both unconsolidated and water-saturated at the time of intrusion. Local stacks of pillow lava are found on the margins of the edifice. More than fifty, 0.5 to 3 m wide dykes intrude CM stratigraphy and display, either, peperitic pillowed margins or sharp, chilled margins and columnar-jointing. Measurements of paleomagnetic directions (9 sites) were made for all CM lithofacies and record a single-pole direction indicating a single monogenetic eruption. A glaciovolcanic origin is strongly suggested by the abundant subaqueous lithofacies (i.e. palagonitized tephra, pillows, peperites) and the physiographic setting of the edifice which is well above any drainage that could sustain a standing body of water. The elevation of CM and depth of surrounding valleys indicate syn-eruptive confinement by a paleo-ice sheet that was ≥850 m thick. The edifice shape, size, and surround- ing topography suggest a ‘leaky’ paleolake system capable of supporting ~0.36 km3 of water. The glacio

Cracked Mountain (CM) is a basaltic volcano within the northern extension of the Cascade volcanic arc into southwest, British Columbia, Canada (i.e. Garibaldi Volcanic Belt) and is dated at 401 ± 38 ka (40Ar/39Ar). The edifice covers an area of ~1.5 km2 and has a volume of 0.18 km3. The volcano features steep margins with local relief of ~250 m (1,650 m a.s.l), is dissected by abundant 0.5 to ~20 m wide extensional cracks with depths up to 30 m, and has a highly eroded top. The edifice is dominated by massive to poorly stratified, moderately to pervasively palagonitized lapilli tuffs, comprising vitric fine ash to lapilli. Juvenile pyroclasts have blocky to highly vesiculated shapes consistent with a phreatomagmatic (i.e. explosive) origin. The lapilli tuffs are intruded by and mingled with coherent to disaggregated lobes of peperitic pillowed lavas. Contacts between lapilli tuff and peperitic pillowed lava show soft-sediment deformation and in-situ quench-fragmentation indicating that the tephra was both unconsolidated and water-saturated at the time of intrusion. Local stacks of pillow lava are found on the margins of the edifice. More than fifty, 0.5 to 3 m wide dykes intrude CM stratigraphy and display, either, peperitic pillowed margins or sharp, chilled margins and columnar-jointing. Measurements of paleomagnetic directions (9 sites) were made for all CM lithofacies and record a single-pole direction indicating a single monogenetic eruption. A glaciovolcanic origin is strongly suggested by the abundant subaqueous lithofacies (i.e. palagonitized tephra, pillows, peperites) and the physiographic setting of the edifice which is well above any drainage that could sustain a standing body of water. The elevation of CM and depth of surrounding valleys indicate syn-eruptive confinement by a paleo-ice sheet that was ≥850 m thick. The edifice shape, size, and surround- ing topography suggest a ‘leaky’ paleolake system capable of supporting ~0.36 km3 of water. The glacio

Cracked Mountain (CM) is a basaltic volcano within the northern extension of the Cascade volcanic arc into southwest, British Columbia, Canada (i.e. Garibaldi Volcanic Belt) and is dated at 401 ± 38 ka (40Ar/39Ar). The edifice covers an area of ~1.5 km2 and has a volume of 0.18 km3. The volcano features steep margins with local relief of ~250 m (1,650 m a.s.l), is dissected by abundant 0.5 to ~20 m wide extensional cracks with depths up to 30 m, and has a highly eroded top. The edifice is dominated by massive to poorly stratified, moderately to pervasively palagonitized lapilli tuffs, comprising vitric fine ash to lapilli. Juvenile pyroclasts have blocky to highly vesiculated shapes consistent with a phreatomagmatic (i.e. explosive) origin. The lapilli tuffs are intruded by and mingled with coherent to disaggregated lobes of peperitic pillowed lavas. Contacts between lapilli tuff and peperitic pillowed lava show soft-sediment deformation and in-situ quench-fragmentation indicating that the tephra was both unconsolidated and water-saturated at the time of intrusion. Local stacks of pillow lava are found on the margins of the edifice. More than fifty, 0.5 to 3 m wide dykes intrude CM stratigraphy and display, either, peperitic pillowed margins or sharp, chilled margins and columnar-jointing. Measurements of paleomagnetic directions (9 sites) were made for all CM lithofacies and record a single-pole direction indicating a single monogenetic eruption. A glaciovolcanic origin is strongly suggested by the abundant subaqueous lithofacies (i.e. palagonitized tephra, pillows, peperites) and the physiographic setting of the edifice which is well above any drainage that could sustain a standing body of water. The elevation of CM and depth of surrounding valleys indicate syn-eruptive confinement by a paleo-ice sheet that was ≥850 m thick. The edifice shape, size, and surround- ing topography suggest a ‘leaky’ paleolake system capable of supporting ~0.36 km3 of water. The glacio

Video showing georreferenced water column echograms collected during the eruption of the submarine volcano occured in 2011. El Hierro island.

An ephemeral (and proximal) outcrop at the quaternary basaltic Puig de la Garrinada cinder volcano was studied in order to decipher eruptive mechanism variations in the course of a single eruption. Once the volcanostratigraphy was established (and recorded by photographs), a very detailed sampling of underlying lava flows, bombs and a large number of fine-sized lapilli and ash beds was carried out. An ad hoc description card was elaborated for study under stereo microscope in order to identify the different types of materials that form the volcanic cone. Ten material types were recognised: sedimentary accidental clasts, massive lava accidental clasts, bombs, xenoliths, xenocrysts and phenocrysts, oxidised scoria, scoria with oxidised film, fluidal pyroclasts, non-fluidal pyroclasts, and coatings. Subsequent studies under SEM + EDS and basic chemical characterization of the samples (whole rock XRF for major and trace elements) and EMPA were conducted. All these studies make possible the reconstruction of the eruptive history of the La Garrinada volcano, which shows a transition from initial strombolian activity to gradually incorporated phreatomagmatic activity. This permits the calculation of magma eruption rates, magma column oscillations and aquifer interactions with magma column. Since our general conclusions agree well with the discrimination of eruptive episodes obtained from the stereo microscope description card, macroscopic volcanostratigraphy and chemical results, it is proposed that a similar study protocol (quick volcanostratigraphy logging, photographic record, detailed sampling, description following this card) might be useful in the reconstruction of eruptive activity of other cinder cones in the Garrotxa region and elsewhere, and therefore can provide a good and quick methodological tool, especially when rapid field description and sampling is required (ephemeral outcrops, risky sampling during active eruptive episodes, etc.). Moreover, the conducted

Primary magmas are generated by 4-6% partial melting near the garnet-spinel stability fields beneath Heimaey (i.e. 80-65 km depth). The magmas fractionate 31% olivine and clinopyroxene en-route to ponding at the base of the crust (and forming a parental Vestmannaeyjar magma). Abundant normally zoned phenocrysts of olivine and plagioclase, in combination with curvilinear trends in major element variation diagrams and heterogeneous isotope ratios (similar to MORB) suggests that the rock suite evolved by fractional crystallization and that crustal contamination and/or magma-mixing was insignificant. Although Heimaey rocks are devoid of clinopyroxene as a phenocryst phase, decreasing ratios of CaO/Al2O3 and Sc/Y with increasing degree of fractionation suggest that clinopyroxene was present as a fractionating phase. The most evolved lava on Heimaey (Eldfell) can be successfully related to the most primitive (Stórhöfði) through 73% fractional crystallization of an olivine + clinopyroxene + plagioclase + titanomagnetite assemblage. Individual magma batches were emplaced into different levels of the crust where they evolved separately from each other prior to eruption. The lack of equilibrium phenocryst assemblages in the Heimaey rocks suggests that the residence times in crustal magma chambers were short. Upon eruption, the pathways used by the rising magma are probably zones of weaknesses associated with extensional stress exerted by the propagating Eastern Volcanic Zone (as indicated by the preferentially aligned eruptive fissures). When magmas erupt in a shallow marine environment, tuff-cones are formed as a result of explosive interactions between magma and water/sediment mixtures. Tuffs comprise about 65% of total erupted volume on Heimaey. The tuff cones deposits consists of normally graded planar air-fall deposits and undulating cross-bedded base-surge deposits, with an increase in frequency of base-surge deposits closer to the vent regions. The distribution of crus