Past Mathematical Geoscience Seminar

7 May 2021
14:00
Olivier Gagliardini
Abstract

The first studies of the friction at the base of glacier were done by the pioneers Weertman and Lliboutry in the 1950s, who proposed theories under assumptions that have not been questioned for decades. Among these assumptions, the most questionable are the 2d geometry of the bumps, the pure sliding at the ice-bed interface and the hypothesis of stationary water pressure. In this seminar, I will present recent works using local modelling of basal friction with the finite element method that explore the validity of the proposed friction laws when these assumptions do not hold any more. 

The join button will be published on the right (Above the view all button) 30 minutes before the seminar starts (login required).

  • Mathematical Geoscience Seminar
12 February 2021
14:00
Abstract

The interplay between fluid flows and fractures is ubiquitous in Nature and technology, from hydraulic fracturing in the shale formation to supraglacial lake drainage in Greenland and hydrofracture on Antarctic ice shelves.

In this talk I will discuss the above three examples, focusing on the scaling laws and their agreement with lab experiments and field observations. As climate warms, the meltwater on Antarctic ice shelves could threaten their structural integrity through propagation of water-driven fractures. We used a combination of machine learning and fracture mechanics to understand the stability of fractures on ice shelves. Our result also indicates that as meltwater inundates the surface of ice shelves in a warm climate, their collapse driven by hydrofracture could significantly influence the flow of the Antarctic Ice Sheets. 

The join button will be published on the right (Above the view all button) 30 minutes before the seminar starts (login required).

  • Mathematical Geoscience Seminar
29 January 2021
14:00
Sam Pegler
Abstract

Deep-marine volcanism drives Earth's most energetic transfers of heat and mass between the crust and the oceans. Yet little is known of the primary source and intensity of the energy release that occurs during seafloor volcanic events owing to the lack of direct observations. Seafloor magmatic activity has nonetheless been correlated in time with the appearance of massive plumes of hydrothermal fluid known as megaplumes. However, the mechanism by which megaplumes form remains a mystery. By utilising observations of pyroclastic deposits on the seafloor, we show that their dispersal required an energy discharge that is sufficiently powerful (1-2 TW) to form a hydrothermal discharge with characteristics that align precisely with those of megaplumes observed to date. The result produces a conclusive link between tephra production, magma extrusion, tephra dispersal and megaplume production. However, the energy flux is too high to be explained by a purely volcanic source (lava heating), and we use our constraints to suggest other more plausible mechanisms for megaplume creation. The talk will cover a combination of new fluid mechanical fundamentals in volcanic transport processes, inversion methods and their implications for volcanism in the deep oceans.

The join button will be published on the right (Above the view all button) 30 minutes before the seminar starts (login required).

  • Mathematical Geoscience Seminar
4 December 2020
14:00
Celine Guervilly
Abstract

Convection is the main heat transport process in the liquid cores of planets and the primary energy source for planetary magnetic fields. These convective motions are thought to be turbulent and strongly constrained by rotation. In this talk, I will discuss the large-scale flows (zonal jets and vortices) that form in this rapidly-rotating turbulent regime, which we explore with numerical models.

The join button will be published on the right (Above the view all button) 30 minutes before the seminar starts (login required).

  • Mathematical Geoscience Seminar
20 November 2020
14:00
Abstract

The classical fractional crystallisation scenario for magma ocean solidification on the Moon suggests that its crust formed by flotation of light anorthite minerals on top of a liquid ocean, which has been used to explain the anorthositic composition of the lunar crust. However, this model points to rapid crustal formation over tens of million years and struggles to predict the age range of primitive ferroan anorthosites from 4.5 and 4.3 Ga. 

Here I will present a new paradigm of slushy magma ocean crystallisation in which crystals are suspended throughout the magma ocean, and the lunar crust forms by magmatic processes over several hundreds of thousand years.

We will then focus on the effects of the particular characteristics of this primary crust on the transport and eruption of magma on the Moon.

The join button will be published on the right (Above the view all button) 30 minutes before the seminar starts (login required).

  • Mathematical Geoscience Seminar
6 November 2020
14:00
Abstract

In this talk, I will present a series of new experimental data, supported by theoretical models, of the transport of ash, aerosols and bubbles in multiphase plumes rising through stratified environments, focussing on the structure of flow and the dispersal of the different phases. The models have relevance for the dispersal of volcanic ash in the atmosphere and ocean, the mixing of aerosols in buildings, and the fate of suspended sediment produced during deep sea mining. 

The join button will be published on the right (Above the view all button) 30 minutes before the seminar starts (login required).

  • Mathematical Geoscience Seminar
23 October 2020
14:00
Colin Meyer
Abstract

Snow densification and meltwater refreezing store water in alpine regions and transform snow into ice on the surface of glaciers. Despite their importance in determining snow-water equivalent and glacier-induced sea level rise, we still lack a complete understanding of the physical mechanisms underlying snow compaction and the infiltration of meltwater into snowpacks. Here we (i) analyze snow compaction experiments as a promising direction for determining the rheology of snow though its many stages of densification and (ii) solve for the motion of refreezing fronts and for the temperature increase due to the release of latent heat, which we compare to temperature observations from the Greenland Ice Sheet (Humphrey et al., 2012). In the first part, we derive a mixture theory for compaction and air flow through the porous snow (cf. Hewitt et al. 2016) to compare against laboratory data (Wang and Baker, 2013). We find that a plastic compaction law explains experimental results. Taking standard forms for the permeability and effective pressure as functions of the porosity, we show that this compaction mode persists for a range of densities and overburden loads (Meyer et al., 2020). We motivate the second part of the talk by the observed melting at high elevations on the Greenland Ice Sheet, which causes the refreezing layers that are observed in ice cores. Our analysis shows that as surface temperatures increase, the capacity for meltwater storage in snow decreases and surface runoff increases leading to sea level rise (Meyer and Hewitt, 2017). Together these studies provide a holistic picture for how snow changes through compaction and the role of meltwater percolation in altering the temperature and density structure of surface snow.

The join button will be published on the right (Above the view all button) 30 minutes before the seminar starts (login required).

  • Mathematical Geoscience Seminar
13 March 2020
14:00
Herbert Huppert
Abstract

World wide, unconstrained lava flows kill people almost each year and cause extensive damage, costing millions of pounds. Defending against lava flows is possible by using topographic variations sensibly, placing buildings considerately, constructing defending walls of appropriate size and the like. Hinton, Hogg and Huppert have recently published three rather mathematical papers outlining how viscous flows down slopes interact with a variety of geometrical shapes; evaluating, in particular, the conditions under which “dry zones” form – safe places for people and belongings – and the size of a protective wall required to defend a given size building.

Following a desktop experimental demonstration, we will discuss these analyses and their consequences.

  • Mathematical Geoscience Seminar
31 January 2020
14:00
Yuri Dumaresq Sobral
Abstract

The collapse of granular columns in a viscous fluid is a common model case for submarine geophysical flows. In immersed granular collapses, dense packings result in slow dynamics and short runout distances, while loose packings are associated with fast dynamics and long runout distances. However, the underlying mechanisms of the triggering and runout, particularly regarding the complex fluid-particle interactions at the pore-scale, are yet to be fully understood. In this study, a three-dimensional approach coupling the Lattice Boltzmann Method and the Discrete Element Method is adopted to investigate the influence of packing density on the collapsing dynamics. The direct numerical simulation of fluid-particle interactions provides evidence of the pore pressure feedback mechanism. In dense cases, a strong arborescent contact force network can form to prevent particles from sliding, resulting in a creeping failure behavior. In contrast, the granular phase is liquefied substantially in loose cases, leading to a rapid and catastrophic failure. Furthermore, hydroplaning can take place in loose cases due to the fast-moving surge front, which reduces the frictional resistance dramatically and thereby results in a longer runout distance. More quantitatively, we are able to linearly correlate the normalized runout distance and the densimetric Froude number across a wide range of length scales, including small-scale numerical/experimental data and large-scale field data.

  • Mathematical Geoscience Seminar

Pages