Lecture 10 - Understanding Volcanic Activity Flashcards
How does Geological Field Mapping help us Understand a Volcano’s past?
-Look at surface rocks
-Define the age of each layer
-Look at size and composition of each layer
-Take measurements and samples for laboratory analysis
-Use surface measurements as a guide for what’s below ground
How do we find out what is Below Ground?
Drilling:
-drill a core
-look at the rock and structures in
the core
Seismic Imaging:
-Send seismic waves into the
ground at a known time
-Seismic waves passing across a
boundary between two rock
types will reflect some of the
energy
-These reflections in the signals
are received, and used to
reconstruct the rock
How does Gas help us to Predict Volcanic Eruptions?
-Volcanoes mostly emit SO2 and CO2
-Changes in emissions provide clues to activity
-Gas composition is directly correlated to magma type
-Gasses may react with water to produce other chemicals
How do Direct Gas Measurements help predict Volcanic Eruptions?
-Gasses are collected directly from fumeroles in an evacuated flask or solution bottle for analysis
-This is a good measure because there is minimal mixing with the atmosphere
-Provides the most detail of volcanic gas composition
-Only can be made when the volcano is not eruptive
How does a Fourier Transform Infrared Spectrometer help predict Volcanic Eruptions?
-Uses infrared spectroscopy
-Rapid, high-precision high rate measurements of gas composition
How do MultiGAS Monitors help predict Volcanic Eruptions?
-Measures multiple gasses at once
-CO2, SO2, H2S
-Also measures temperature and pressure
-Uses optical and electrochemical sensors
-Measurements in quiet times give an average baseline
-Measurements during an eruption giver early-warning clues for next time
-Monitors are carried to fumeroles and placed down-wind
-They provide samples every minute which avoids the need to send samples to a lab
How does Gas-DOAS help predict Volcanic Eruptions?
-Differential Optical Absorption Spectroscopy
-Detects UV radiation (SO2 absorbs UV)
-DOAS monitor is pointed at the sun; the lower the UV signal compared to usual, the more SO2 is present
-By comparing DOAS measurements near a fumerole/ plume and how far away you are, you can precisely measure how much SO2 is being emitted
Describe the Nature of SO2 gas
-SO2 is released from magma at shallow depths
-This indicates there is magma near the surface (the volcano could erupt soon)
-SO2 dissolves easily in water so it could be hard to measure if volcano is surrounded by water bodies
Describe the Nature of Hydrogen Sulphide
-SO2 mixes with groundwater to produce H2S
-This means there is enough groundwater to react with all the SO2 (suggests quiet behaviour as not much SO2 is being emitted)
-Measured by taking a gas sample and measuring the gas in a lab
How do CO2 Soil Efflux Monitors help to predict Volcano Eruptions?
-Measures volume of CO2 diffused into soil
-Lots of measurements from many sites are required to get an accurate idea of how much is released
Horseshoe lake, Mammoth Mt.
-Lots of plant dieback due to root
suffocation
-Linked with CO2
-Flux of CO2 changes every 2
years linked to minor
earthquakes
-CO2 escapes from deeper in the Earth
-Increase in CO2 could indicate new magma is arriving from depth
How does Water Chemistry help predict Volcanic Eruptions?
-Collecting water samples of local rivers/streams
-Measure composition in the lab
-Chlorine content is a good indicator of increased activity (linked to amount of water interacting with magma)
How does a Tiltmeter help to predict Volcanic Eruptions?
-Uses a sensitive inclinometer to measure ground level rising/ falling
-Can detect tilts the equivalent of placing a pence piece under 1 end of a plank a mile long
-Buried underground 1-6cm
How does GPS help predict Volcanic Eruptions?
-Uses satellites and a series of ground-based GPS instruments
-These report their position to a constellation of satellites
-This can reveal changes in height and lateral position on the Earth’s surface
How does InSAR help to predict Volcaninc Eruptions?
-Interferometric Synthetic Aperture Radar
-Shoots bursts of radar waves at the ground
-Measures time between emission and detection
-Uses height of the satellite and speed of light to figure out the height of the ground
-Second pass of the ground (1 orbit around Earth) reveals if the ground level is changing
-High accuracy but low repetitions (satellites can take weeks or months to pass round the Earth
How do Strainmeters help predict Volcanic Eruptions?
-Strain = change in size/shape
-Detect ground warping and local slope change
-High sensitivity (can detect changes in atmospheric pressure from passing weather fronts), so they must be buried more than 10m underground
-Earthquakes or magma movement deforms the ground and the instrument
