Seminar archive

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# Tuesday 11th June 2013, 4.30pm – Marie Edmonds

Unlocking the secrets of melt inclusions at Kilauea Volcano

Venue: Tilley Lecture Theatre, Earth Sciences Department

Melt inclusions from 25 eruptions of Kilauea Volcano over the last 600 years highlight the important processes of fractionation, mixing and degassing prior to eruption. The sampled eruptions span a large range of styles, ranging from effusive through to transient explosive and fountaining. The data show that there is a statistical difference in the geochemistry between the different styles, and through different time periods at Kilauea, suggesting that the explosivity of melts might be “set” right from the point of separation from the mantle source. We look at one fountaining eruption in detail (the 1959 Kilauea Iki eruption) to investigate how fountains are triggered. Inputs of hot, primitive, gas-rich melts mix with cooler, stored melts, causing rapid vesiculation, leading to fountains. Along the way, we see how melt inclusions are dramatically altered by processes such as post-entrapment crystallization and the development of a shrinkage bubble, illustrating some of the pitfalls of melt inclusion work.

# Thursday 23rd May 2013, 1.00pm – Katherine Daniels

Thermal models of dyke intrusion during development of Continent-Ocean Transition

Venue: Harker II, Geology Department

A consensus has emerged in recent years from a variety of geoscientific disciplines that extension during continental rifting is achieved only partly by plate stretching: dyke intrusion also plays an important role. Magma intrusion can accommodate extension at lower yield stresses than are required to extend thick, strong, unmodified continental lithosphere mechanically, thereby aiding the breakup process. Dyke intrusion is also expected to thermally modify the rheology of the extending plate, but the extent of its influence and the timescales over which it operates are poorly understood.

To address this issue, a numerical solution to the heat flow equation is developed here to quantify the thermal effects of dyke intrusion on the continental crust during rifting. Finite difference models demonstrate that magmatic extension rate exerts a first order control on crustal thermal structure.Once dyke intrusion supersedes faulting and stretching as the principal extensional mechanism the crust will heat and weaken rapidly (<<1 Ma). The thermal models are benchmarked against a priori constraints on crustal structure and dyke intrusion episodes in Ethiopia.

# Wednesday 7th November 2012, 5.30pm – Nial Peters and Yves Moussallam

Eruption en tu boca! Chile 2012 Volcanic monitoring at Villarrica, Puyehue and Lascar volcanoes

Venue: Harker II, Geology Department

Abstract not available

# Tuesday 30th October 2012, 7.30pm – Yves Moussallam and Nial Peters

Organised by Cambridge University Caving Club

Volcanic Caves

Venue: ALB, Clare Hall, Herschel Road

Abstract not available

# Wednesday 24th October 2012, 5.00pm – Brendan McCormick and Lois Salem

Santorini and CVG field trip to the Etna & the Aeolian

Venue: Harker II, Geology Department

Brendan will be talking about his recent fieldwork on Santorini with colleagues from Oxford and Lois about our recent CVG field trip to the Etna & the Aeolian Islands The talks will be followed by a glass of wine in the Common Room at 17:30 ish. The keen amongst us can then head off to a pub and/or for a curry after.

# Friday 7th September 2012, 4.00pm – Dr Chiara Maria Petrone (University of Cambridge)

The volcanic activity of Stromboli volcano: magma dynamics of a steady-state volcano

Venue: Harker II, Geology Department

Abstract not available

# Tuesday 12th June 2012, 1.00pm – David Neave & Margaret Hartley

The Record of Deep Magmatic Processes in the AD 1783 Laki Fires Eruption, Iceland.

Venue: Tilley Lecture Theatre, Earth Sciences Department

A report on the results of studies into crystal-melt relationships, concurrent mixing and crystallisation and ongoing investigation of deep degassing behaviour.

# Thursday 24th May 2012, 5.00pm – Sara Mana (Rutgers University)

Rifting of a Continent: the North Tanzanian Divergence Zone, East African Rift System

Venue: Harker II, Geology Department

The role of magmatism in continental rift initiation and evolution is of much debate. Our research focuses on a section of the magmatic-rich eastern branch of the East African Rift in Northern Tanzania that depicts the complex early stage of tectono-magmatic rift evolution. This area, the North Tanzania Divergence (NTD), is currently volcanically active with a magmatic history that initiated in the Miocene, prior to documented extension. Some of the NTD volcanoes are among Earth’s largest (Kilimanjaro, Ngorongoro), and have produced a diverse array of lavas from basalt to rhyolite, trachyte, nephelinite to phonolite and carbonatite. Their distribution is widespread, both N-S along the rift axis and E-W across the valley floor and onto the adjacent rift margins.

The oldest NTD magmatism is recorded at the centrally located Essimingor volcano. We report new 40Ar/39Ar ages, major and trace element analyses and Sr-Nd-Pb radiogenic isotopic signatures on well-located lavas representing the observable variation in lithology and stratigraphy from the S and SW slopes of Essimingor. Laser-incremental heating 40Ar/39Ar analyses of whole rock, matrix and nepheline separates yield plateau ages ranging from 5.76±0.02 Ma to 5.91±0.01 Ma.

Essimingor major element data define narrow compositional variations consistent with fractional crystallization. Open system processes of mixing or contamination are inferred from an increase in Sr isotopic values with indices of fractionation. Ce/Pb varies over a large range (59 to 7), the lower end of which implies crustal assimilation that overprints the mantle signature. An FC versus AFC process has therefore been modeled. The Sr-Nd-Pb isotopic values indicate the involvement of a HIMU-like component. Trace element abundances of the more primitive samples (MgO >9 wt%) suggest partial melting of a metasomatized lithospheric mantle peridotite characterized by the presence of residual garnet and phlogopite combined with minor amphibole and apatite. The coexistence of garnet and phlogopite in the source suggests melting at ~80–150 km depth, consistent with the base of the lithosphere in the eastern branch identified using Rayleigh wave tomography (120-160 km; Weeraratne et al. 2003) and indicating that Essimingor represents the initial phase of lithospheric removal.

Ongoing analysis of younger NTD volcanoes should help constrain the timing and location of the progressive lithospheric thinning during early rifting.

# Monday 21st May 2012, 2.15pm – Dr Mario Montopoli, Dept. Geography, University of Cambridge,

This talk is part of the Centre for Atmospheric Science seminars series

Microwave remote sensing of volcanic ash clouds.

Venue: Unilever Lecture Theatre, Department of Chemistry

Plinian and sub-Plinian volcanic explosive eruptions probably represent one
of the most devastating natural events for the surrounding environment,
endangering people’s lives and property. Explosive volcanic eruptions can
significantly influence climate as well as cloud formation and global
circulation through atmospheric transport. Volcanic ash clouds are also an
increasing hazard to aviation safety because of growing airline traffic.

From the first rudimental visual inspections at the times of Pliny the

Elder, the human curiosity and its needs to find effective countermeasures
to these extreme volcanic episodes has never ceased, even though their
(fortunate) rarity makes the scientific research quite challenging.

Nowadays, visual inspections are accompanied by sophisticated measurements
made by direct analysis and from remote sensors. Microphysical
characterization of the Plinian volcanic ash plumes is usually carried out
by analyzing tephra deposits and ash sedimentation at ground. This analysis
may only give indirect information on the ash cloud composition as several
processes can take place during the ash fallout. On the other hand,
real-time monitoring of a volcano eruption is not always possible by
conventional visual inspections due to the usual low optical visibility.
Finally, airborne flights within ash plumes using sample probes, as done
for water clouds, are considered too dangerous for the safety reasons
previously mentioned. Remote sensing techniques represent a unique tool to
be exploited for this scope. They allow observing the evolution of some key
parameters of volcanic eruptions without a direct interaction between the
measurement system and the target of the measure. Electromagnetic or
acoustic waves are usually used to this aim. Among the available remote
sensing techniques, satellite-based approaches, using multi-frequency
radiometers with visible and infrared channels, have demonstrated to be a
valuable supports to the monitoring of ash clouds. Moreover, measurements
in the visible spectral window are not always available due to its solar
illumination dependence and the optical thickness of volcanic clouds can
severely impair the sounding of lower cloud layers.

In contrast with satellite methodologies, ground-based microwave scanning
weather radars can gather three-dimensional information of ash-cloud
scattering volumes with ranges up to several hundreds of kilometers, in all
weather conditions, at a fairly high spatial resolution (hundreds of
meters) and with a repetition cycle of few minutes. So far, these systems
have been mainly used for meteorological operational forecasts and for
observing of some small number of volcanic areas which can be monitored by
previously installed instruments. There are also several open issues about
microwave weather radar capabilities to detect and quantitatively retrieve
ash cloud parameters.

After a basic introduction on remote sensing principles, the presentation
will focus at illustrating and assessing the potential and limitation of
microwave remote sensing of Plinian and sub-Plinian volcanic eruption. This
will be done using examples from both ground based radar and satellite
radiometers data, collected after the 2010 and 2011 eruptions in Iceland.
Some quantitative estimates of ash category and ash concentration will be
shown together with explanations of the algorithms used.

# Friday 18th May 2012, 1.00pm – Clive Oppenheimer

Volcanoes on borders

Venue: Seminar room, Departement of Geography main building, Downing Site

I’ll give a report of recent visits to two interesting volcanoes, both situated on international borders: Paektu/Changbai (Democratic People’s Republic of Korea, aka North Korea, and China) and Nabro (Eritrea and Ethiopia). The borders aspect does add complexity to risk management and emergency response issues, which I shall touch on, but I’ll mostly focus on the travelogue.