Coarse Lapilli Research Articles

Total grain-size distribution of four subplinian–Plinian tephras from Hekla volcano, Iceland: Implications for sedimentation dynamics and eruption source parameters

The size distribution of the population of particles injected into the atmosphere during a volcanic explosive eruption, i.e., the total grain-size distribution (TGSD), can provide important insights into fragmentation efficiency and is a fundamental source parameter for models of tephra dispersal and sedimentation. Recent volcanic crisis (e.g. Eyjafjallajökull 2010, Iceland and Córdon Caulle 2011, Chile) and the ensuing economic losses, highlighted the need for a better constraint of eruption source parameters to be used in real-time forecasting of ash dispersal (e.g., mass eruption rate, plume height, particle features), with a special focus on the scarcity of published TGSD in the scientific literature. Here we present TGSD data associated with Hekla volcano, which has been very active in the last few thousands of years and is located on critical aviation routes. In particular, we have reconstructed the TGSD of the initial subplinian–Plinian phases of four historical eruptions, covering a range of magma composition (andesite to rhyolite), eruption intensity (VEI 4 to 5), and erupted volume (0.2 to 1km3). All four eruptions have bimodal TGSDs with mass fraction of fine ash (<63μm; m63) from 0.11 to 0.25. The two Plinian dacitic-rhyolitic Hekla deposits have higher abundances of fine ash, and hence larger m63 values, than their andesitic subplinian equivalents, probably a function of more intense and efficient primary fragmentation. Due to differences in plume height, this contrast is not seen in samples from individual sites, especially in the near field, where lapilli have a wider spatial coverage in the Plinian deposits. The distribution of pyroclast sizes in Plinian versus subplinian falls reflects competing influences of more efficient fragmentation (e.g., producing larger amounts of fine ash) versus more efficient particle transport related to higher and more vigorous plumes, displacing relatively coarse lapilli farther down the dispersal axis.

Using satellite radar amplitude imaging for monitoring syn-eruptive changes in surface morphology at an ice-capped stratovolcano

Satellite-based measurements of synthetic aperture radar amplitude provide a method for monitoring volcanoes during unrest and eruptions even when visual observations are not possible, for example due to poor weather or at night, and when radar phase measurements are noisy or decorrelated. Here, we use high resolution radar amplitude images from the TerraSAR-X and COSMO SkyMed satellites to investigate surface changes associated with explosive eruptions of Cotopaxi volcano, Ecuador in August 2015. We generate change difference and amplitude ratio maps spanning the start of explosive activity at Cotopaxi, which show complex spatial variations in radar amplitude both on and around the summit ice-cap that we attribute to a number of processes related to the eruption. Observed amplitude decreases are caused by crater deepening, ashfall onto ice and surface smoothing by ashfall onto slopes facing away from the satellite, while amplitude increases are due to deposition of coarse lapilli and wet tephra, increased soil saturation due to geothermally driven glacier melting, and smoothing of slopes facing towards the satellite. We discuss the potential applications of radar amplitude images for monitoring and hazard evaluation at active volcanoes.

Pómez Bosque de Tlalpan, producto de una erupción de gran magnitud en el margen suroeste de la cuenca de México

In this contribution we describe a white pumice fall deposit, informally named pómez Bosque de Tlalpan (PBT), found in several outcrops in the southern Mexico basin. The most representative sequence occurs at the Bosque de Tlalpan park, Delegación Tlalpan, in Mexico City. In this site the deposit is 3 m thick, massive, and contains 80–90 vol. % of pumice clasts, predominantly of coarse lapilli-sized and some block-sized fragments. The PBT has a dacitic composition (64.9–66 wt. % SiO2, on anhydrous basis) of calc-alkaline affinity, and a mineral assemblage represented by plagioclase &gt; amphibole &gt; orthopyroxene &gt; biotite, ±Fe-Ti oxides, with quartz in lesser proportions, and zircon as accesory mineral, in a vesicular and glassy matrix. According to data collected from seven outcrops, thickness and clast size of the deposit decrease towards the NE and therefore the vent source should be located to the SW of Bosque de Tlalpan. Possible sources are the volcanoes Ajusco and San Miguel, which are part of the Sierra de Las Cruces volcanic range, and are located in this direction at ~11 km from Bosque de Tlalpan. The age of the PBT deposit was determined by radiocarbon dating of underlying paleosoils that yielded 25,730 ± 130 to 37,450 ± 330 yrs B.P. (Late Pleistocene). Additionally, thermoluminscence dating of one sample yielded an age of 30,300 ± 5,000 years, similar to the radiocarbon ages. Hence, the PBT represents the youngest reported deposit from the Sierra de Las Cruces volcanic range. Although only seven outcrops were described in this work, we interpret the PBT deposit as produced by a plinian-type eruption, based on its massive structure, its ca. 3 m thickness, and the presence of pumice clasts in coarse lapilli to block sizes, as well as 3.5 cm sized lithics, at 11 km from the possible vent source, characteristic of this kind of deposits. We discard the monogenetic volcanoes from the Chichinautzin volcanic field as the vent source of the PBT deposit, because this kind of volcanoes is relatively mafic in composition and do not produce plinian-type deposits.

Syn- and post-fragmentation textures in submarine pyroclasts from Lō`ihi Seamount, Hawai`i

The extent and timing of vesiculation and microlite formation in ascending basaltic melts are relatively well understood for subaerial eruptions, but they have not been studied thoroughly for submarine eruptions. This is largely due to a lack of samples of appropriate volume and grain size. We present a quantitative textural evaluation of coarse lapilli from two cone-forming deposits at ∼ 1 km depth on Lō`ihi Seamount, Hawai`i, collected during a sampling-intensive submersible dive series in 2006. Lapilli from the deposits, named the northern and southern cones, have modal bulk vesicularities of 55 and 42%, respectively, and vesicle populations dominated by sub-spherical, non-interconnected vesicles, with number densities on the order of 10 4 to 10 5 cm − 3 . Clasts of modal vesicularity have margin-parallel zonation, with seawater-quenched rims interpreted to preserve “syn-fragmentation” magmatic textures in microlite-free sideromelane glass enclosing “post-fragmentation” tachylitic interiors with vesicle and microlite textures that progressively coarsen from rim-to-core. Degassing scenarios are linked to syn-fragmentation vesicle textures to demonstrate that both magmas degassed in dominantly closed systems. Diffusion-controlled cooling rates of basaltic pyroclasts in contact with water are linked to post-fragmentation evolution of vesicle and microlite textures to make inferences about transportation and dispersal of the pyroclasts in low submarine jets. The textural analysis shows that the northern and southern cone eruptions were not strictly analogous to any classical subaerial eruption type. They were uniquely submarine, with ambient seawater playing a crucial role in the processes of degassing, vesiculation, crystallization, and dispersal.

Clast size controls and longevity of Pleistocene desert pavements at Lathrop Wells and Red Cone volcanoes, southern Nevada

Research Article| July 01, 2006 Clast size controls and longevity of Pleistocene desert pavements at Lathrop Wells and Red Cone volcanoes, southern Nevada Greg A. Valentine; Greg A. Valentine 1Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Charles D. Harrington Charles D. Harrington 1Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Greg A. Valentine 1Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Charles D. Harrington 1Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Publisher: Geological Society of America Received: 13 Dec 2005 Revision Received: 09 Feb 2006 Accepted: 03 Apr 2006 First Online: 09 Mar 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 The Geological Society of America, Inc. Geology (2006) 34 (7): 533–536. https://doi.org/10.1130/G22481.1 Article history Received: 13 Dec 2005 Revision Received: 09 Feb 2006 Accepted: 03 Apr 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Greg A. Valentine, Charles D. Harrington; Clast size controls and longevity of Pleistocene desert pavements at Lathrop Wells and Red Cone volcanoes, southern Nevada. Geology 2006;; 34 (7): 533–536. doi: https://doi.org/10.1130/G22481.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Formation of desert pavement and accretionary soils are intimately linked in arid environments. Well-sorted fallout scoria lapilli at Lathrop Wells (75–80 ka) and Red Cone (ca. 1 Ma) volcanoes (southern Nevada) formed an excellent parent material for pavement, allowing infiltration of eolian silt and fine sand that first clogged the pore space of underlying tephra and then aggraded and developed vesicular A (Av) horizons. Variations in original pyroclast sizes provide insight into minimum and maximum clast sizes that promote pavement and soil formation: pavement becomes ineffective when clasts can saltate under the strongest winds, while clasts larger than coarse lapilli are unable to form an interlocking pavement that promotes silt accumulation (necessary for Av development). Contrary to predictions that all pavements above altitudes of ∼400 m would have been reset in their development after late Pleistocene vegetation advances, the soils and pavements show clear differences in maturity between the two volcanoes. This indicates that either the pavements and/or soils develop slowly over many tens of thousands of years and then are very stable, or, if they are disrupted by vegetation advances, subsequent pavements are re-established with successively more mature characteristics. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Clast size controls and longevity of Pleistocene desert pavements at Lathrop Wells and Red Cone volcanoes, southern Nevada

Formation of desert pavement and accretionary soils are intimately linked in arid environments. Well-sorted fallout scoria lapilli at Lathrop Wells (75‐80 ka) and Red Cone (ca. 1 Ma) volcanoes (southern Nevada) formed an excellent parent material for pavement, allowing infiltration of eolian silt and fine sand that first clogged the pore space of underlying tephra and then aggraded and developed vesicular A (Av) horizons. Variations in original pyroclast sizes provide insight into minimum and maximum clast sizes that promote pavement and soil formation: pavement becomes ineffective when clasts can saltate under the strongest winds, while clasts larger than coarse lapilli are unable to form an interlocking pavement that promotes silt accumulation (necessary for Av development). Contrary to predictions that all pavements above altitudes of !400 m would have been reset in their development after late Pleistocene vegetation advances, the soils and pavements show clear differences in maturity between the two volcanoes. This indicates that either the pavements and/or soils develop slowly over many tens of thousands of years and then are very stable, or, if they are disrupted by vegetation advances, subsequent pavements are re-established with successively more mature characteristics.

Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP

The Mawson Formation and correlatives in the Transantarctic Mountains and South Africa record an early eruption episode related to the onset of Ferrar-Karoo flood basalt volcanism. Mawson Formation rocks at Coombs Hills comprise mainly (≥80% vol) structureless tuff breccia and coarse lapilli tuff cut by irregular dikes and sills, within a large vent complex (>30 km2). Quenched juvenile fragments of generally low but variable vesicularity, accretionary lapilli and country rock clasts within vent-fill, and pyroclastic density current deposits point to explosive interaction of basalt with groundwater in porous country rock and wet vent filling debris. Metre-scale dikes and pods of coherent basalt in places merge imperceptibly into peperite and then into surrounding breccia. Steeply dipping to sub-vertical depositional contacts juxtapose volcaniclastic rocks of contrasting componentry and grainsize. These sub-vertical tuff breccia zones are inferred to have formed when jets of debris + steam + water passed through unconsolidated vent-filling deposits. These jets of debris may have sometimes breached the surface to form subaerial tephra jets which fed subaerial pyroclastic density currents and fall deposits. Others, however, probably died out within vent fill before reaching the surface, allowing mixing and recycling of clasts which never reached the atmosphere. Most of the ejecta that did escape the debris-filled vents was rapidly recycled as vents broadened via lateral quarrying of country rock and bedded pyroclastic vent-rim deposits, which collapsed along the margins into individual vents. The unstratified, poorly sorted deposits comprising most of the complex are capped by tuff, lapilli tuff and tuff breccia beds inferred to have been deposited on the floor of the vent complex by pyroclastic density currents. Development of the extensive Coombs Hills vent-complex involved interaction of large volumes of magma and water. We infer that recycling of water, as well as recycling of pyroclasts, was important in maintaining water supply for phreatomagmatic interactions even when aquifer rock in the vent walls lay far from eruption sites as a consequence of vent-complex widening. The proportion of recycled water increased with vent-complex size in the same way that the proportion of recycled tephra did. Though water recycling leaves no direct rock record, the volcaniclastic deposits within the vent complex show through their lithofacies/structural architecture, lithofacies characteristics, and particle properties clear evidence for extensive and varied recycling of material as the complex evolved.

Scoria cone construction mechanisms, Lathrop Wells volcano, southern Nevada, USA

Abstract Scoria cones are commonly assumed to have been constructed by the accumulation of ballistically ejected clasts from discrete, relatively coarse-grained Strombolian bursts and subsequent avalanching such that the cone slopes are at or near the angle of repose for loose scoria. The cone at the hawaiitic Lathrop Wells volcano, southern Nevada, contains deposits that are consistent with these processes during early cone-building phases; these early deposits are composed mainly of coarse lapilli and fluidal bombs and are partially welded, indicating relatively little cooling during flight. However, the bulk of the cone is composed of relatively fine-grained (ash and lapilli) planar beds with no welding, even within a few tens of meters of the vent. This facies is consistent with deposition by direct fallout from sustained eruption columns of relatively well-fragmented material, primarily mantling cone slopes and with a lesser degree of avalanching than is commonly assumed. A laterally extensive fallout deposit (as much as 20 km from the vent) is inferred to have formed contemporaneously with these later cone deposits. This additional mechanism for construction of scoria cones may also be important at other locations, particularly where the magmas are relatively high in volatile content and where conditions promote the formation of abundant microlites in the rising mafic magma.

Scoria cone construction mechanisms, Lathrop Wells volcano, southern Nevada, USA

Research Article| August 01, 2005 Scoria cone construction mechanisms, Lathrop Wells volcano, southern Nevada, USA Greg A. Valentine; Greg A. Valentine 1 Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Don Krier; Don Krier 1 Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Frank V. Perry; Frank V. Perry 1 Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Grant Heiken Grant Heiken 1 Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Greg A. Valentine 1 Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Don Krier 1 Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Frank V. Perry 1 Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Grant Heiken 1 Earth and Environmental Sciences Division, M.S. D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Publisher: Geological Society of America Received: 25 Feb 2005 Revision Received: 14 Apr 2005 Accepted: 18 Apr 2005 First Online: 03 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 The Geological Society of America, Inc. Geology (2005) 33 (8): 629–632. https://doi.org/10.1130/G21459AR.1 Article history Received: 25 Feb 2005 Revision Received: 14 Apr 2005 Accepted: 18 Apr 2005 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Greg A. Valentine, Don Krier, Frank V. Perry, Grant Heiken; Scoria cone construction mechanisms, Lathrop Wells volcano, southern Nevada, USA. Geology 2005;; 33 (8): 629–632. doi: https://doi.org/10.1130/G21459AR.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Scoria cones are commonly assumed to have been constructed by the accumulation of ballistically ejected clasts from discrete, relatively coarse-grained Strombolian bursts and subsequent avalanching such that the cone slopes are at or near the angle of repose for loose scoria. The cone at the hawaiitic Lathrop Wells volcano, southern Nevada, contains deposits that are consistent with these processes during early cone-building phases; these early deposits are composed mainly of coarse lapilli and fluidal bombs and are partially welded, indicating relatively little cooling during flight. However, the bulk of the cone is composed of relatively fine-grained (ash and lapilli) planar beds with no welding, even within a few tens of meters of the vent. This facies is consistent with deposition by direct fallout from sustained eruption columns of relatively well-fragmented material, primarily mantling cone slopes and with a lesser degree of avalanching than is commonly assumed. A laterally extensive fallout deposit (as much as 20 km from the vent) is inferred to have formed contemporaneously with these later cone deposits. This additional mechanism for construction of scoria cones may also be important at other locations, particularly where the magmas are relatively high in volatile content and where conditions promote the formation of abundant microlites in the rising mafic magma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The influence of surface volcaniclastic layers from Haleakala (Maui, Hawaii) on soil water conservation

This study focuses on the soils and surficial volcaniclastic layers of Haleakala's crater (Maui, Hawaii). The main objective is to assess the effects of covers with fragments of various sizes (ash, cinder, lapilli) on soil water conservation. Soil and gravel samples were collected in Haleakala National Park from a site at 2505 m where the Hawaiian silversword, a giant rosette-plant, grows densely on pyroclastic materials. An evaporation experiment lasting 22 days showed a gradual drop in seven pairs of soil samples initially at field capacity. One set of samples was left bare, the other was covered by gravel mulches (GM); these resulted in lengthening of T 100% (total desiccation time) by a factor of 2.3–5.2. Bare soils dried after 70–140 h, but drying time under gravel was 246–509 h. Mean grain size ( M z) and sorting ( φ σ ) had the greatest influence on evaporation rates. Coarse lapilli ( M z: 13.8 mm) were less effective than fine ash ( M z: 2.9–3.8 mm) in preventing water losses, while medium-grained cinder ( M z: 4–5.2 mm) produced the greatest water savings. Lapilli (mean φ σ : 0.48) and ash ( φ σ : 0.6) were moderately- to well-sorted; cinders, with a broader grain-size range ( φ σ : 1.13), were poorly sorted. This allowed infilling of large interstices between coarse fragments by smaller grains, effectively reducing pore size and therefore evaporation rates. A second experiment determined water storage and rates of water loss by mulches. Wetting occurred swiftly, within 3–4 min. All gravel types were dry within 26 h. This drying process is important for water conservation, as it effectively prevents further water loss from the mulch surface. Larger fragments stored less water. This is related to their `surface area/weight' ratio, which increases for smaller particles. Thus, fine ash or cinder grains, with a high total area, intercept more water than larger lapilli. A 5-cm thick layer of ash intercepted an average of ∼6.8 mm of rain, slightly more than the same depth of cinder (6.3 mm), but lapilli retained only 4.7 mm. Therefore, light rainfall events are more likely to contribute water to soil under lapilli than below finer pyroclastic material. Volcaniclastic covers serve an important ecological role in Haleakala by prolonging periods of water availability to plants, thus allowing Hawaiian silverswords to grow for longer time spans.

Discrimination of eolian and pyroclastic-surge processes in the generation of cross-bedded tuffs, Jemez Mountains volcanic field, New Mexico

Discrimination of pyroclastic deposits emplaced by volcanic processes and reworked pyroclastic sediments is a primary objective of studies in volcaniclastic strata. Cross-bedded tuffs of both eolian and pyroclastic-surge origins are identified within the late Miocene Peralta Tuff Member of the Bearhead Rhyolite, in north-central New Mexico. Distribution, paleoflow directions, grain-size characteristics, and depositional structures permit discrimination of these two similar facies. Eolian tuffs exhibit structures diagnostic of eolian sands, are relatively well sorted, and lack both the fine ash and coarse lapilli and bombs typically found in surge deposits. Discrimination between eolian reworked and primary surge pyroclastic deposits is critical for volcanic hazard studies near modern volcanoes and for correct interpretation of proximity to vents in ancient volcaniclastic sequences.