Geology topics

Christopher Harpel

Publications and source records attributed to Christopher Harpel.

7 recordsLinked to original sources

USGS2024

The Khonkho tephra: A large-magnitude volcanic eruption coincided with the rise of Tiwanaku in the Andes

We report a tephra deposit in the southern Lake Titicaca Basin, Bolivia, which was deposited by a major, previously unrecognized eruption sometime between AD 400 and 720. Archaeological data suggest these centuries were characterized by a substantial community migration to Tiwanaku, where social interaction networks gave birth to one of the Andes’ first large complex societies. Here we provide an initial characterization of this tephra, based on samples from the archaeological site Khonkho Wankane. The same tephra is present at two other archaeological sites in the region. Given the great distance to the nearest active volcano, this tephra layer likely derives from a large-magnitude, Late-Holocene explosive eruption of a Central Andean volcano. We suggest that this major event be included in the human history of the region, given its inferred magnitude and wide dispersal area. Future research could confirm the Khonkho tephra at other sites, identify the source volcano, estimate its volume, and more precisely date the eruption.

southern Lake Titicaca Basin↗

USGS2024

To mix or not to mix: Details of magma storage, recharge, and remobilization during the Pacheco stage at Misti Volcano, Peru (≤21–2 ka)

We investigate ten of the most recent tephra-fall deposits emplaced between ≤21–2 ka from the Pacheco stage of Misti volcano, Peru, to elucidate magma dynamics and explosive eruption triggers related to magma storage, recharge, and remobilization. Whole-rock, glass, and mineral textures and compositions indicate the presence of broadly felsic, intermediate, and mafic magmas in a chemically and thermally stratified magma storage system (Zones 1–3) that interact to differing extents prior to eruption. Intermediate magmas are defined by plagioclase + amphibole + two-pyroxenes + Fe-Ti oxides and phase equilibria indicate they formed at ~300–600 MPa and ~950–1000 °C. Intermediate magmas dominate the Pacheco stage and either erupted alone as hybridized magmas or mingled with minor volumes of cool felsic magmas (~800 °C) in which only plagioclase + Fe-Ti oxides are stable. Felsic magmas do not exclusively comprise any tephra-fall deposit emplaced during the Pacheco stage but were remobilized by recharge and mixing with intermediate magmas in order to erupt. Furthermore, felsic-hosted amphibole cognate to the intermediate magmas are reacted despite the felsic magmas being water saturated, which suggests they are staged above the amphibole stability limit (≤200 MPa). The cryptic presence of mafic magmas is indicated by high-An plagioclase cores (An 74–88 ), rare anhedral olivine (Fo 77–80 ), and possibly high Mg# augite and amphibole (up to Mg# 84 and 77, respectively). The dearth of basalt to basaltic andesite melts recorded in erupted glasses and exclusivity of high-An plagioclase to crystal cores signals mafic magmas are staged deeper in the crust than the intermediate magmas. Periodic interactions between these magmas tracked via glass compositions and crystal exchange reveal an alternation between the production of mingled magmas and their eruption shortly after a recharge event, followed by a period of homogenization and eruption of hybridized magmas. As such, we identify magma recharge as a key mechanism by which half of the explosive eruptions were triggered in the Pacheco stage. A >100 °C increase in Misti’s fumarole temperatures from 1967 to 2018 coincident with changes in fumarolic gas composition is consistent with degassing of a mafic recharge magma, signaling that Misti could produce similar explosive eruptions in the future.

Misti Volcano↗

USGS2023

The late Pleistocene Sacarosa tephra-fall deposit, Misti Volcano, Arequipa, Peru: Its magma, eruption, and implications for past and future activity

Between 38.5 ka cal BP and 32.4 ka cal BP, a dacitic Volcanic Explosivity Index 5 eruption at Misti volcano emplaced the Sacarosa tephra-fall deposit. Its biotite phenocrysts, fine grain size, scarce lithics, and abundant loose crystals characterize the deposit at locations sampled. The eruption’s ~ 800 °C magma rose rapidly from ~ 10 km depth, culminating in a Plinian eruption which reached a mass eruption rate of 7.7 × 10 6 –4.1 × 10 7 kg/s and emplaced about 3 km 3 of tephra within tens of hours. The unit comprises two layers of subequal thickness separated by a diffuse contact with the upper distinguished by being slightly coarser and less well sorted than the lower. The deposit’s coarser upper layer indicates either climactic conditions or a lesser degree of fragmentation during the latter half of the eruption. Strong winds distributed the deposit southwest of Misti, where it crops out over at least 800 km 2 and drapes the present site of Arequipa with up to 100 cm of tephra. The Sacarosa deposit is the first among the Cayma stage deposits, a distinctive group of felsic, biotite-bearing units, to be carefully described and its eruption characterized. Several Cayma stage deposits were emplaced by voluminous explosive eruptions similar to the Sacarosa eruption, representing a ~ 8.9–15.5 ky interval of powerful eruptions. Such an explosive eruption today would threaten Arequipa’s over 1,100,000 residents, many of whom live within the Sacarosa deposit’s distribution.

Misti Volcano↗

USGS2022

Nuevos datos: Avalancha de escombros de Acajutla, volcán Santa Ana

The Acajutla debris-avalanche deposit is dated to about 40,000 cal BP. The dating is based on two 14C dates on pieces of wood from the debris-avalanche deposit recovered from a core at the Santa Águeda School Center. The debris-avalanche deposit overlies a 1.2-m-thick paleosol and four ash layers. One of these ash layers is geochemically correlated to the Los Chocoyos ash from Atitlán Caldera, while the others are possibly from eruptions of Coatepeque and Ilopango Calderas. The new data, collected in well reports from the years 1966 to 2019, include deposit thicknesses identified in 25 wells for water monitoring, bathymetric data from nautical charts, GEBCO’s grids, updated topographic data from LIDAR, and a reassessment of the deposit’s lateral limits. This new data will allow us to better constrain the volume of the Acajutla debris-avalanche deposit.

Conference Paper↗

USGS2022

Estratigrafía preliminar del flanco Este del volcán de Santa Ana

We present the eruption sequence for the east flank of Santa Ana volcano, which we divide into the sections above and below the Tierra Blanca Joven (TBJ) formation. The sequence below the TBJ suggests a series of mafic magmatic eruptions that began before 7,800 cal BP and continued until after 5,800 cal BP. These eruptions emplaced tephra-fall and pyroclastic-density-current deposits. The sequence above the TBJ are deposits from recent eruptions during the last 1.5 ky. Most of these eruptions were phreatomagmatic with associated pyroclastic surges. The two sequences demonstrate a shift in eruptive style possibly related to an increase in water volume in the hydrothermal system.

Santa Ana volcano↗

USGS2021

Azorella compacta's long-term growth rate, longevity, and potential for dating geomorphological and archaeological features in the arid southern Peruvian Andes

We determine the long-term growth rate and longevity of an Azorella compacta growing on Misti volcano, near Arequipa, Peru to investigate the species' capacity as a geochronological resource. Using 14 C dating on stem pieces sequestered within the plant's cushion, which grows larger through time, we obtain ages of 15 ± 15 14 C yrs BP and 165 ± 15 14 C yrs BP at depths of 15 cm and 29 cm below the cushion's living surface, respectively. Applying a mixed calibration curve with a Bayesian growth model yields calendar age ranges of 1948–1958 CE and 1802–1935 CE for our 14 C dates, respectively. Such ages provide sufficiently precise constraints for investigations requiring dating during the last few hundred years when individual 14 C dates yield imprecise calendar age ranges. We infer a long-term growth rate of 1.3–3.5 mm yr −1 , corroborating published maximum short-term growth rates. Extrapolating our growth model to the A. compacta 's core suggests that it began growing as early as 1462–1830 CE. At such age it lived through myriad important geological and historical events, including regional earthquakes, volcanic unrest at Misti, decades to centuries of the Little Ice Age, and a broad transect of Peruvian history possibly beginning during the Inca Empire. A. compacta may provide another important geochronological resource in the arid Central Andes that can be applied to date volcanological, glacial, mass-movement, and archaeological features, especially where dendrochronology and lichenometry are not possible.

Peruvian Andes↗

USGS2019

The Orange Tuff: A Late Pleistocene tephra-fall deposit emplaced by a VEI 5 silicic Plinian eruption in West Java, Indonesia

A VEI 5 dacite eruption emplaced the Orange Tuff about between 34.3 cal kBP and 17.2 cal kBP. Gunung Salak is the unit’s source and the Orange Tuff represents the most recent such eruption from any of the volcanoes southwest of Bogor, Indonesia. The Orange Tuff is the region’s first such documented tephra-fall deposit whose characteristics and phenocryst geochemistry make it readily identifiable over at least 1250 km 2 . Magnetite compositions and temperature and f O 2 estimates inferred from Fe-Ti oxide compositions are particularly useful for identifying the unit. Deposit characteristics suggest that the eruption lasted 1–11 h with mass eruption rates of 1.0–8.3 × 10 8 kg/s and a column height of 31–40 km. The eruption’s column height and the deposit’s 2.5–11 km 3 volume suggest that the unit was dispersed over a much wider area than mapped. The unit is a marker bed throughout its mapped distribution and has potential to be applied over a much broader area as a regional marker bed. The large population and infrastructure proximal to Salak suggest that the unit should be considered in hazards assessments despite its age and the lack of subsequent similar eruptions.

Bulletin of Volcanology↗