J. E. Guest’s research while affiliated with University College London and other places

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Publications (169)


Chapter 9 The volcanic history of Furnas Volcano, Sao Miguel, Azores
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September 2015

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369 Reads

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34 Citations

Geological Society London Memoirs

J. E. GUEST

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Furnas is the easternmost of the trachytic active central volcanoes of Sa˜o Miguel. Unlike the other central volcanoes, Sete Cidades and Fogo, Furnas does not have a substantial edifice built up above sea-level. Although not as dominant as the other two volcanoes, Furnas does, however, have an edifice rising from the basal basaltic lavas exposed on the north coast to around 600 m asl on the northern rim of the main caldera. In common with Sete Cidades and Fogo, Furnas had major trachytic explosive eruptions in its volcanic history that emplaced welded ignimbrites. In the last 5 ka Furnas has had 10 moderately explosive trachytic eruptions of sub-Plinian character; two of these have taken place since the island was settled in the mid-fifteenth century. A future eruption of sub-Plinian magnitude is a major hazard posed by Furnas Volcano. Even when not in eruption, Furnas is a hazardous environment. Its fumarolic fields discharge high levels of CO2 and concentrations in some area of Furnas village present a risk to health; the steep slopes and poorly consolidated volcanic materials are prone to landslides, in particular when triggered by earthquakes or following heavy rain, as was the case in 1997, when landslides caused severe damage and casualties in Ribeira Quente.


Chapter 1 Volcanic geology of Sao Miguel Island (Azores Archipelago): introduction
  • Article
  • Full-text available

September 2015

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1,463 Reads

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18 Citations

Geological Society London Memoirs

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Chapter 7 Eruptive history and evolution of Sete Cidades Volcano, Sao Miguel Island, Azores

September 2015

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222 Reads

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37 Citations

Geological Society London Memoirs

Sete Cidades is an active central volcano on the western part of São Miguel. The geological record reveals that subaerial activity started more than 250 ka ago. Stratigraphic units defined for Sete Cidades deposits reflect major events in the history of the volcano and are organized into two main groups: the Inferior Group and the Superior Group. Caldera formation resulted from three major paroxysmal events that occurred at about 36, 29 and 16 ka ago. Analysis of the eruptive history of Sete Cidades shows that effusive or moderately explosive eruptions, of Hawaiian and/or Strombolian styles, were located on the slopes of the central volcano. Conversely, trachytic explosive activity is mostly centred inside the caldera involving, in a first stage, predominantly Plinian and sub-Plinian phenomena, changing about 5 ka ago to a dominant hydromagmatic style. Trachytic effusive eruptions are represented by domes and associated lava flows that crop out in the inner caldera walls and on the western slopes of the volcano. Offshore submarine activity is represented by the historic Surtseyan eruptions of 1638 and 1811. In the last 5 ka Sete Cidades was the most active central volcano in the Azores with 17 explosive eruptions predominantly with hydromagmatic character.


Chapter 10 Distribution and significance of basaltic eruptive centres: Sao Miguel, Azores

September 2015

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94 Reads

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33 Citations

Geological Society London Memoirs

Basaltic volcanism occurs at all the active volcanic systems of São Miguel. For the last 30 ka, the eruption of basaltic magma has been particularly significant in the areas between the three polygenetic volcanoes – Sete Cidades, Fogo and Furnas – and two basaltic fields have developed: the Picos Fissural Volcanic System (PFVS) and the Congro Fissural Volcanic System (CFVS). About 5 ka ago volcanic activity at CFVS ended abruptly and since then almost all basaltic activity has been concentrated at the PFVS, where about 30 eruptions have taken place. Despite the absence of eruptive activity, the Congro system represents one of the most active seismic areas in the archipelago. It shows episodes of volcanic deformation that are indicative of magma ascent, which halted beneath the volcanic system. Two historical eruptions are associated with the PFVS. The 1563 eruption at Pico do Sapateiro was of basaltic composition, whereas that of the 1652 eruption was, for almost two centuries, also considered to be basaltic. This event had, however, a Vulcanian style and involved the production of large amounts of fine ash and the growth of three trachyte domes with associated coulées. It was accurately described in contemporary historical accounts.


Eruptive frequency and volcanic hazards zonation in Sao Miguel Island, Azores

September 2015

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241 Reads

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31 Citations

Geological Society London Memoirs

São Miguel Island comprises five active volcanic systems, including three central volcanoes with calderas and two basaltic fissure systems. Volcanic eruptions in São Miguel are of basaltic and trachytic nature (s.l.), including Hawaiian, Strombolian, sub-Plinian, Plinian and Vulcanian events, the more explosive ones frequently including hydromagmatic phases. Large Plinian eruptions are related to caldera-forming events that occurred in the past. With reference to the Fogo A stratigraphic marker, a total of 73 individual volcanic eruptions have been identified in the last 5 ka, giving a recurrence interval of 68.5 years. Taking into account that only six events have occurred in historical times, the recurrence interval increases to 95 years and, clearly, a future event is overdue because the most recent eruption occurred in 1652. It should be noted, however, that some volcanic eruptions in the past have occurred in clusters. The eruptive frequencies of the last 5 ka of activity have been determined for all types of eruptions and related hazards, including lava flows, pyroclastic falls, pyroclastic density currents (PDCs) and lahars. The areas susceptible to volcanic products have been mapped and modelled under different eruptive conditions.


Chapter 8 Eruptive history of Fogo Volcano, Sao Miguel, Azores

September 2015

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237 Reads

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41 Citations

Geological Society London Memoirs

Fogo is the largest of the three active central volcanoes on São Miguel and dominates the centre of the island. It is located at the intersection of NW–SE, NE–SW and east–west-trending fault systems, showing a complex morphology with a Summit Caldera formed as a result of explosive and collapse events. The edifice of Fogo has been extensively dissected by erosion, with deep valleys that show clear tectonic control. The products of Fogo range from basalt to trachyte and belong to a potassic alkaline suite. The oldest subaerial products of Fogo are .200 ka. Older products are poorly exposed, making stratigraphic correlation difficult, particularly on the north flank where considerable subsidence within the NW–SE Ribeira Grande graben has occurred. A more complete stratigraphy for the last 40 ka was established on the southern flank of the volcano. During this period there were large trachytic Plinian eruptions, including those of the Ribeira Chã (8–12 ka BP) and Fogo A (4.6 ka BP). The last intracaldera eruption was historic and occurred in 1563, and 4 days afterwards there was an effusive basaltic eruption on the northwestern lower flank of the volcano.


Chapter 11 The older volcanic complexes of Sao Miguel, Azores: Nordeste and Povoacao

September 2015

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155 Reads

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19 Citations

Geological Society London Memoirs

The oldest part of São Miguel is to the east of Furnas. Previous research argued that these volcanics belong to a construct called the Nordeste Volcano, a heavily eroded shield which not only extends to the east coast of the island but also underlies Furnas Volcano in the west. On the basis of geomorphological mapping, we argue that Nordeste comprises two volcanic systems: an older Nordeste construct (the Nordeste Volcanic System) and the younger Povoação Volcano that straddles the Nordeste shield on its western margin. The Nordeste Volcanic System consists of the Lower Basalts which constitute the overwhelming majority of its subaerial products that are exposed in coastal cliff sections. Above the Lower Basalts is a surficial drape of ankaramites and the Upper Basalts. There is no evidence of large explosive trachytic eruptions from Nordeste Volcanic System. Povoação Volcano comprises an early shield construct, after which the volcano experienced caldera collapse. Post-caldera deposits are poorly exposed, but include basaltic, mugearitic and trachytic lavas intercalated by cut-and-fill sequences. Radiometric dating has yet to resolve fully the absolute ages of the Nordeste and Povoação volcanic systems, but morphology indicates that the former is much older than the latter.


Effect of slope on development of pahoehoe flow fields: Evidence from Mount Etna

March 2012

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89 Reads

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28 Citations

Journal of Volcanology and Geothermal Research

We describe and compare two types of pahoehoe on Mount Etna: one similar to an Hawaiian inflated flow field consisting of tumuli, lava rises and lava rise pits; and the other a coalescing complex of rootless centres of ephemeral boccas fed from lava tubes and superimposed on an initial 'a'a flow field. The former we define as a primary pahoehoe field that results from relatively slow advance rate of lava over an almost horizontal surface. The latter is a result of an eruption of long enough duration to allow tube formation over a substantial portion of the flow field over steeper slopes; at breaks in slope in the underlying topography centres of ephemeral boccas develop giving rise to low effusion rate pahoehoe lavas covering the original channelled 'a'a surface. These we refer to as secondary pahoehoe flow fields.Highlights► Characterisation of two types of pahoehoe textured flow fields, Mount Etna. ► These are defined as primary and secondary pahoehoe flow fields. ► Slope angle is determined as a critical factor in generation of pahoehoe texture.


Volcanism and resurfacing on Venus at the full resolution of Magellan SAR data

August 2010

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13 Reads

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11 Citations

We examine the importance of localized volcanism in resurfacing on Venus by analyzing the results of geologic mapping of a 12° × 12° area at the full resolution of Magellan SAR data. Resurfacing due to corona-, ridge-, and small volcano-related volcanism accounts for 27%, 6%, and 10% respectively of the mapped area. Mapping at the resolution of Magellan data, rather than a regional scale, gives corona-related flow unit areas that can differ individually by almost an order of magnitude, with a total increase of 28%, and more than three times as many identifiable units. A total of 2919 small volcanoes or vents less than 10 km in diameter were identified in the F-Map, with a mean diameter of 1.59 (s.d. = 1.08) km and densities of up to 36 small volcanoes per 50 km2. Taken together, coronae, ridge eruptions, and small volcanoes probably make a significant contribution to resurfacing on Venus.


Stratigraphy and composition of lava flows in Mare Nubium and Mare Cognitum

January 2010

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115 Reads

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20 Citations

Meteoritics & Planetary Science

Three major periods of basaltic activity characterize the infill of the basins. Each of these periods was itself punctuated by discrete phases of widespread magma eruptions: three during both the Late Imbrian Epoch and the early Eratosthenian Period and then two in the late Eratosthenian Period. We found the youngest lavas off the eastern border of the Fra Mauro peninsula and, mantling a much larger area, over most of the central western Nubium basin. Our results place the Nubium/Cognitum basalts in the low‐Ti category (1–5 wt% TiO 2 ). The data indicate that the majority (˜90%) of the mare terrain has iron content between 18 and 22 wt%. In particular, FeO contents tend to concentrate toward two compositional poles, each of ˜20 wt%, and a much smaller one of ˜15 wt%. These values are typical of nearside lunar maria. To complement our compositional data, we present a census of craters larger than 500 m using Orbiter IV images. The result was a crater count average with frequency 5.6 × 10 ⁻² km ⁻² , translating into an inferred mean age of 3300 Ma for the exposed lava flows. By combining lava chemistry with age, we find a possible correlation between the ages of the most prominent flow units and their estimated titanium content, with younger basalts becoming progressively Ti‐richer with time (from 2–3 to 4–5 wt% TiO 2 ).


Citations (68)


... The creation and provision of maps of areas prone to volcanic eruption disasters, including volcanic hazard risk zones and volcanic geological maps are essential to understand potential hazards. Location maps showing ground motion and cold lava flow from the eruption of Mount Merapi and Mount Marapi can be seen in Figs. 4 and 5. Governments and volcanological institutions must monitor volcanic activity using specialized equipment such as seismographs and tiltmeters [21,22]. The government has established clear and organized procedures to deal with emergency situations such as the eruption of Mount Merapi. ...

Reference:

Lessons learnt from community preparedness for Mount Merapi and Mount Marapi eruption disasters
The increasing exposure of cities to the effects of volcanic eruptions: A global survey
  • Citing Article
  • January 2000

Environmental Hazards

... Ignimbrites (here defined loosely as pyroclastic density current BPDC^ deposits consisting dominantly of a poorly sorted mixture dominated by juvenile pumice and ash, e.g., Branney and Kokelaar 2002) are widespread along arc, back-arc, and continental intraplate regions that erupt evolved magmas (e.g., phonolites, trachytes, rhyolites). Large ignimbrites have also been identified at several oceanic intraplate settings, including at the Canary Islands (Freundt and Schmincke 1995), the Azores (e.g., Duncan et al. 1999), and Cape Verde (Eisele et al. 2015). Along the Canary Islands, this type of volcanic activity has produced many hundreds of cubic kilometer of deposits. ...

Furnas Volcano, Sao Miguel, Azores - Introduction
  • Citing Article
  • September 1999

Journal of Volcanology and Geothermal Research

... The Capelinhos cone was emplaced as a typical Surtseyan cone (Cole et al., 1996(Cole et al., , 2001 on the western-most end of Faial Island ( Figure 1a) by an eruption extending over 13 months (September 1957-November 1958 (Machado et al., 1962;Cole et al., 1996Cole et al., , 2001. Borges (2004) quantified the Capelinhos rate of shoreline retreat until the year 1981 by assessing post-eruptive coastal development (Machado and Freire, 1985). ...

Capelinhos: The disappearing volcano
  • Citing Article
  • January 1996

Geology Today

... The internal, younger (12 -10 ka bp) caldera is smaller, having dimensions of about 4.5 Â 3.5 km. The collapse-related formation of these two calderas was followed by periods of eruptive infilling (Booth et al. 1978;Gaspar et al. 1995;Guest et al. 1999). Within the internal caldera there are two depressions related to more recent eruption collapses: one contains the Furnas crater lake and the second the village of Furnas (c. ...

Evolução morfoestrutural do Vulcão das Furnas (ilha de S. Miguel, Açores)
  • Citing Article
  • January 1995

... More recently, on 1 January 1980, an earthquake of magnitude 7.2 ML has mostly devastated Terceira Island (Hirn et al., 1980;Silva, 2005). Subaerial volcanic eruptions have ranged from Hawaiian to sub-Plinian style, while submarine ones have been mainly of Surtseyan type (Gaspar et al., 2015a(Gaspar et al., , 2015b. ...

Chapter 1 Volcanic geology of Sao Miguel Island (Azores Archipelago): introduction

Geological Society London Memoirs

... The eastern part of the island is formed by the older volcanic systems of Povoação and Nordeste (>878 ka; Johnson et al., 1998) (Figure 3a), which are considered extinct. Although their stratigraphy is poorly understood and radiometric dating has yet to resolve their chronology, it is thought that they have not erupted in at least several hundred thousand years (Johnson et al., 1998;Duncan et al., 2015). The active central volcanoes of São Miguel are characterised by explosive trachytic volcanism of Plinian and sub-Plinian style, while basaltic Hawaiian/Strombolian eruptions dominate in the fissure systems. ...

Chapter 11 The older volcanic complexes of Sao Miguel, Azores: Nordeste and Povoacao
  • Citing Chapter
  • September 2015

Geological Society London Memoirs

... The Fogo and Sete Cidades volcanoes were chosen for lava block collection ( Fig. 1). Fogo Volcano (> 200,000 years), occupies 150 km² at the centre of the island, rises 947 m above sea level (asl) and features a 3.2 km diameter caldera hosting a lake at its summit (Wallenstein et al., 2015). Fogo volcano has an active high-temperature geothermal field in its northern flank and the last unrest period, marked by seismic activity and ground deformation, was attributed to magmatic intrusion, hydrothermal fluid ascension, or both (Trota, 2009;Silva et al., 2012;Okada et al., 2015;D'Araújo et al., 2022a, b). ...

Chapter 8 Eruptive history of Fogo Volcano, Sao Miguel, Azores
  • Citing Chapter
  • September 2015

Geological Society London Memoirs

... Lagoa das Furnas crater lake is located inside the more recent caldera of Furnas Volcano (10-12,000 years old, Guest et al., 2015), the easternmost of the three active central volcanoes that dominate the geology of São Miguel Island ( Fig. 1a-b). The caldera is characterised by fault systems trending WNW-ESE, NE-SW, N-S and NNW-SSE. ...

Chapter 9 The volcanic history of Furnas Volcano, Sao Miguel, Azores
  • Citing Chapter
  • September 2015

Geological Society London Memoirs

... Lake Prata (37 • 48′23″N, 25 • 44′12″W; 520 m a.s.l.; Fig. 1D) is found on the island of São Miguel, more precisely in the western sector of the Picos fissure system, 5 km SE of the Sete Cidades caldera (Fig. 1C), and it fills the crater of a scoria cone older than 5000 years ( Fig. 1D; Ferreira et al., 2015;Moore and Rubin, 1991). ...

Chapter 10 Distribution and significance of basaltic eruptive centres: Sao Miguel, Azores
  • Citing Chapter
  • September 2015

Geological Society London Memoirs

... The island has a total of 133,390 inhabitants (INE 2021), divided into six municipalities: Lagoa, Nordeste, Ponta Delgada, Povoação, Ribeira Grande and Vila Franca do Campo (Fig. 1b). There are three active central volcanoes on the island, all with summit calderas: Furnas Volcano (Guest et al. 1999, Fogo Volcano (Wallenstein 1999;Wallenstein et al. 2015) and Sete Cidades Volcano (Queiroz 1997;Queiroz et al. 2015). Landslides commonly occur in distinct morphologic structures characterised by steep slopes, such as the inner walls of calderas volcanoes, fault scarps, sea cliffs and stream valleys, mostly composed of non-cohesive materials (pumice deposits) (Fig. 2a). ...

Chapter 7 Eruptive history and evolution of Sete Cidades Volcano, Sao Miguel Island, Azores
  • Citing Chapter
  • September 2015

Geological Society London Memoirs