On the Margins of Ghana and Kawkaw: Four seasons of excavation at Tongo Maaré Diabal (AD 500-1150), Mali

This article summarises the results of four seasons of excavation at Tongo Maaré Diabal (AD 500-1150), near Douentza, Mali. Deep stratigraphic excavations were directed by MacDonald and Togola in 1993, 1995 and by MacDonald in 1996. Complementary, large exposure excavations of the abandonment layer were undertaken by Gestrich in 2010. The combined excavation results speak to topics of craft specialisation, trade, and social organisation. They provide evidence of a specialised blacksmithing community situated at the margins of early Middle Niger and Niger Bend statehood and urbanisation.Le présent article porte sur les résultats de quatre saisons de fouilles sur le site de Tongo Maaré Diabal (AD 500-1150), non loin de la ville de Douentza au Mali. Des fouilles stratigraphiques en profondeur ont été réalisées par MacDonald et Togola en 1993 et 1995 ; et par MacDonald en 1996. Des fouilles complémentaires du dernier horizon d’occupation ont été réalisées sur une grande surface par Gestrich en 2010. Les résultats de ces campagnes portent sur des thèmes de la spécialisation artisanale, du commerce et de l’organisation sociale. Ils nous permettent de décrire une communauté des métallurgistes spécialisées, située en marges des anciens développements étatiques et urbains du Moyen Niger et de la Boucle du Niger.This article is in English

Acoustic and seismic signature of sustained volcanic eruptions

Dissertation (Ph.D.) University of Alaska Fairbanks, 2022Volcanic eruptions of any size can pose a significant risk to the life and livelihood of humans, as well as to infrastructure and the economy. Understanding the dynamics of an eruption is crucial to providing timely and accurate assessments of the eruption and associated hazard. Ideally the monitoring of volcanic unrest and eruption dynamics is done remotely to minimize exposure to volcanologists and maximize the spatial monitoring coverage of instruments. Another important factor is to have real-time data to facilitate rapid analysis and interpretation. Seismic and acoustic (infrasound) waves have proven useful in terms of remote real-time volcano monitoring. However, accurate interpretation of these signals is a challenge due to the complexity of each volcano and each eruption. In this dissertation I present three projects that aim to improve the interpretation of seismic and acoustic signals, specifically their spectral properties, generated by multiphase flow during an eruption. In Chapter 2 we derive a seismic tremor model for a source underground but above the fragmentation level where the gas and particles rush through the volcanic conduit. This physical model assumes ash particles and gas turbulence impact the conduit wall and exert a force that generates seismic waves and is recorded as eruption tremor. We show that it is possible to model the seismic spectral amplitude and shape of a large sustained volcanic eruption, the eruption of Pavlof Volcano in 2016, with particle impacts and turbulence as seismic sources. Our modeling provides a framework to 1) narrow down the parameters associated with eruption dynamics and source processes, and 2) highlight that seismic amplitude and mass eruption rate are not necessarily correlated. Both findings are crucial for the successful interpretation of seismic data during a sustained eruption. In Chapter 3 we move further up above the vent to investigate the acoustic expression of sustained eruptions. The rapid discharge of the multiphase flow through the relatively small vent has been successfully compared to jetting in the past. We develop an algorithm to automatically fit laboratory-derived jet noise spectral shapes (similarity spectra) to the spectrum of three volcanic eruptions: Mount St. Helens 2005, Tungurahua 2006 and Kīlauea 2018. Our quantitative analysis of the misfit between the jet noise spectra and volcanic eruption shows that: 1) the jet noise spectra show a very good fit during the eruption, so we can assume it produces a volcanic form of jet noise, 2) we can distinguish between non-eruptive noise and eruption by the higher misfit of the former and the lower misfit of the latter, and 3) changes in spectral shape correspond to changes in eruption dynamics, which are highlighted by changes in the misfit in time and frequency space. To further look into how changes in spectral properties correspond to changes in eruption dynamics, Chapter 4 focuses in detail on the eruption of fissure 8 on Kilauea volcano in 2018. With the knowledge that the eruption produced jet noise (Chapter 3) we apply jet noise scaling laws and develop a model that relates the changes in infrasound amplitude and peak frequency to changes in jet velocity and diameter. Our analysis shows that in mid-June the infrasound amplitude peaks and the peak frequency decreases. Our jet noise scaling model explains this change through a decrease in jet velocity and increase in jet diameter. This interpretation fits video observations that show a decrease in lava fountain height and a widening of the fountain base around the same time. Our work demonstrates the potential to estimate lava fountain dimensions from infrasound recordings that could be useful for real-time, remote monitoring.NSF Grant EAR-1901614 and EAR-1847736Chapter 1. General introduction -- 1.1. How volcanoes work - a short overview -- 1.1.1. Hawaiian and strombolian -- 1.1.2. Vulcanian -- 1.1.3. Plinian -- 1.2. Eruption monitoring -- 1.2.1. Hazards -- 1.2.2. Seismology -- 1.2.3. Infrasound -- 1.3. Overview on dissertation chapters -- 1.3.1. Chapter 2: A physical model for volcanic eruption tremor -- 1.3.2. Chapter 3: Fitting jet noise similarity spectra to volcano infrasound data -- 1.3.3. Chapter 4: Lava fountain jet noise during the eruption of Ahu'ailā'au, Kīlauea volcano. Chapter 2. A physical model for volcanic eruption tremor -- 2.1. Abstract -- 2.2. Introduction -- 2.3. Data and observations -- 2.4. Model and methods -- 2.4.1. Green's function -- 2.4.2. Particle impacts -- 2.4.3. Turbulence -- 2.4.4. Total power spectral density -- 2.4.5. Parameter estimation -- 2.5. Model results -- 2.5.1. Comparison to river models -- 2.5.2. Parameter sensitivity -- 2.5.3. Mass eruption rate -- 2.5.4. Comparison to the pavlof 2016 spectrum -- 2.6. Discussion -- 2.7. Conclusion. Chapter 3. Fitting jet noise similarity spectra to volcano infrasound data -- 3.1. Abstract -- 3.2. Introduction -- 3.3. Methods -- 3.3.1. Similarity spectra equations -- 3.3.2. Fitting method -- 3.4. Data -- 3.4.1. Mount St. Helens -- 3.4.2. Tungurahua -- 3.4.3. Kilauea 2018 -- 3.4.4. Eruption spectrum -- 3.4.5. Importance of frequency band width -- 3.5. Results & discussion -- 3.5.1. Model fit during eruptions -- 3.5.2. Eruption vs. background noise -- 3.6. Conclusion. Chapter 4. Lava fountain jet noise during the 2018 eruption of fissure 8 of Kīlauea Volcano -- 4.1. Abstract -- 4.2. Introduction -- 4.3. Background -- 4.3.1. Lava fountain dynamics -- 4.3.2. The 2018 lower east rift zone eruption of Kīlauea -- 4.3.3. Jet noise -- 4.4. Data -- 4.4.1. Remote sensing data -- 4.4.2. Infrasound -- 4.5. Methods -- 4.5.1. Infrasound processing -- 4.5.2. Topographic effects -- 4.5.3. Jet noise scaling model -- 4.6. Results -- 4.6.1. UAS observations -- 4.6.2. Infrasound -- 4.6.3. Topographic effects -- 4.6.4. Jet noise fitting -- 4.6.5. Jet noise scaling model -- 4.6.6. Discussion -- 4.7. Conclusion. Chapter 5. General conclusion -- 5.1. Future and ongoing work -- 5.1.1. Jet noise experiments -- 5.1.2. Stromboli -- 5.1.3. Other collaborations -- 5.2. Concluding remarks

Pearl millet and iron in the West African Sahel: Archaeobotanical investigation at Tongo Maaré Diabal, Mali

Recent archaeobotanical analysis revealed that the botanical remains from the site of Tongo Maaré Diabal (Mali) are composed primarily of pearl millet remains (up to 85%). Contemporaneous West African sites (500–1200 Cal AD) usually display more diverse patterns, especially by the end of this period. Indeed, contemporary urban sites of the West African Sahel often comprise combined and diversified farming systems of millet (Pennisetum glaucum), African rice (Oryza glaberrima), sorghum (Sorghum bicolor), Echinochloa sp. and fonio (Digitatia exilis). This article seeks to explain the near-exclusive focus of Tongo Maaré Diabal’s agricultural economy on millet, particularly with regard to the site’s status as a settlement of iron workers

Разработка искровых коммутаторов с циркуляцией газа для ГИН Аркадьева-Маркса

Спроектирован и собран управляемый искровой разрядник с циркуляцией газа и инициированием на принципе "искажения поля" для генератора импульсных напряжений Аркадьева - Маркса. Впервые получены данные о ресурсе работы электродов из нержавеющей стали многоступенчатого разрядника в газе под давлением при работе в генераторе Аркадьева–Маркса в длительном режиме с частотой следования импульсов от 5 до 8 имп/сек. с энергией в импульсе 2 кДж.A controlled spark gap with gas circulation and initiation on the "field distortion" principle for the Arkadiev-Marx pulse voltage generator was designed and assembled. For the first time, data were obtained on the operating life of stainless steel electrodes of a multistage spark gap in a pressurized gas when operating in the Arkadev-Marx generator in a long-time regime with a pulse repetition rate of 5 to 8 pulses per second. with a pulse energy of 2 kJ

Playing God? Synthetic biology as a theological and ethical challenge

In the ethical debate over synthetic biology the formula “playing god” is widely used in order to attack this new branch of biotechnology. The article analyses, contextualizes and criticises this usage with respect to the theological concepts of creation, sin and humans as created in the image of God. Against the background of these theological understandings an ethical corridor of how to responsibly cope with the societal challenges of synthetic biology is presented