This module covers the processes involved in the formation of a volcanic eruption. It delves into the different types of volcano, eruption and products as well as the different risks associated with eruptions and how humans attempt to mitigate against them.
CSM 3070 Volcanology
“The study of the generation and movement of molten rock on Earth (and
other planetary bodies), primarily through volcanoes and volcanic
eruptions, encompassing the generation of magma, its geochemistry and
movement through the Earth’s crust, the physics of volcanic eruptions,
and their hazards and mitigation.”
W1
Introduction
Introduce and explore all aspects of the volcanic system, from melt
generation to eruption products.
Focus not just on the physical/geological aspects, but also the socio-
economic aspects of hazard and risk.
Expect some physics and maths, but also some qualitative analysis too.
✏️
Lecture 1 - introduction
What is volcanology?
The study of the generation and movement of molten rock on Earth (and other planetary
bodies), primarily through volcanoes and volcanic eruptions, encompassing the generation
of magma, its geochemistry and movement through the Earth’s crust, the physics of volcanic
eruptions, and their hazards and mitigation.
Volcanic eruptions are rare; ration of intrusive to extrusive igneous rock = 10:1
imbalance in energy that creates tectonic movement causes eruption in this dynamic earth
system.
eruptions link the geospher to the biosphere, atmosphere and in larger eruptions the
stratosphere, aiding recycling off earth materials.
one eruption will not produce all these hazards
risk increases with increasing populaation and urbanisation
Volcano→ the vent that develops when magma erupts on to the earths surface, the surface
expression of a deeper and more complex network of magma.
Volcanic systems;
magmatic system- the volcano and the ground proccesses below it (inferred from geophysical
research)
melt production → transport → magma storage→ shallow transport and eruption
,hydrothermal system (phreatic eruption, steam)
Differet landforms = variation in eruptoon style, frequence, plate setting. Distribution of
volcanoes and diversity of magma compositions has strong influence of volcano hazard and
risk. Chemicl composition of magma creates variation in magmas physical characteristics
therefpre how the magma acts. different settings also casue differnt types of melt generation.
Volcanoes also vary in duration (hours-decades) as well as the precursors (unrest that then
leads to an eruption) or unrest.
floods, dorughts and earthquakes tend to have a maximum size compared to volcanoes.
W2
Magma generation, migration and storage
what causes rocks to melt
how tectonic settings influences the style of rock melting and magma
produced
how marma migrates from a mantle source through the mantle and into
the crust
✏️
Lecture 2
Magma→ Naturally occurring, fully or partially molten rock material generated within a
planetary body, consisting of melt with or without crystals and gas bubbles and containing a
high enough proportion of melt to be capable of intrusion and extrusion
rocks have a range of minerals therefore a range of melting points, giving rise to the solidus
and liquidus (point of first and last melting of minerals within the rock) hence partial melting.
rock melting
raise the temperature (actually quite rare & difficult)
decrompression melting- due to convection (decrease the presure but temperature remains
fairly constant.
Flux melting- something that changes the melting point. Eg adding water will shift the
solidus and liquidus temperatures and increase the solidus and liquidus range, therefore there
is a greater range for partial melting to occur.
Melting and plate tectonics
1. Divergent boundaries; basalt dominates
o decompresiona partial melting of the uppem mantle
, o ascent speed of mantle rise is key becasue as they rise, they cool. if they rise
slowly then they will cool down and freeze due to haet conduction. if it is fast
enough enough melt is generated.
o in continental rifts we can also generte rhyolite due to crustal contamination
2. hotspots; surface expression of entire mantle plume (originate from the core/mantle
boundary so super hot
o dominantly basalt (flood basalts)
o decompression partial melting and adiabatic expansion
o immobile so a good reference for plate movement, directon and speed
3. convergent boundaries→ difference in melts due to assecion through different plate
types/ country rock
1. island arc; andesite > basalt and basaltic andesite > dacite and rhyolite
basalt ponds of lithosphere and in crust fracitonal crystallisation.
2. continental arc; andesite > dacite and rhyolite > basalt and basaltic andesite
work through a thicker crustal collumn, longer time to mix.
interactoion of maga with crust creates a diverse set of magmas.
o flux melting- water saturated sediments are puled down during subduction. the
fluids are heated and transported into the mantle wedge, producing basalt
initially. Hydroud minerals on the oceanaic crust also release water.
Melt Segregation (movement/ segregation from the source)
Melt accumulates at the top of the melt zone. Buoyancy of the melt compared to the partial
melt below creates a diapir.
it is also hot so has a lower viscosity than its surroundings. Heat conduction to the
surrounding zone gives rise to the behaviour of a fluid. Surrounding rock is forced to move
downward as the diapir rises.
Velocity is negative in the deformation zone as rock is forced to move down.
(strongest control is the deformation zone width, reltated to the temperature and size of
diapir)
Once a diapir cannot go any higher (loss of bupyancy- neutral buoyancy ot rock) it will
spread laterally. The strain rate (speed of change of length) increases in the country rock and
diapir and moves from viscous to brittle deforation and fracturing. This leads to the formation
of dykes. MAgma flows into a fracture initiating a dyke.
Speed of flow of magma into the crack is controlled by thre amount of melt feeding the dyke,
crack width and magma viscosity.
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