VO L3: How do we prevent Destruction from Eruptions?

Question 1

What is our goal in monitoring volcanoes and trying to predict volcanic eruptions?

Answer 1

to reduce losses of life and infrastructure

Question 2

How do we answer: What are the percentages of magmas of different silica contents that have erupted in the past?

Answer 2

Analyses of the chemical components of the eruptive products, like the weight percentage of SiO_2.

Question 3

What do we use to answer this: what is the frequency at which the volcano has erupted in the past?

Answer 3

Radiometric dating techniques such as potassium-argon, argon-argon methods to date young eruptive material

Question 4

What is the ideal baseline data and real-time monitoring situation oh an active or potentially active volcano?

Why is this not realistic?

Answer 4

Ideally, should begin long before eruption starts.

But sampling, mapping, and installing specialized monitoring equipment all take time, money, and political will. In reality, many monitoring schemes are not started until a volcano shows obvious signs of an imminent eruption, or until after an unexpected eruption occurs. This is especially true in the economically under-developed countries where funds are scarce.

Question 5

What is a volcanic hazards map?

Answer 5

Shows zones of likely eruptive activity, and specific hazards.

Question 6

How are volcanic hazards maps made?

Answer 6

Spatial data for a volcano, such as the distribution of eruptive units, are plotted on a geologic map. The map is then used to identify hazards, based on past history, and to produce a volcanic hazards map

Question 7

Rising magma typically will cause what?

Answer 7

Swarms of earthquakes and other types of seismic events, cause swelling or subsidence of volcano’s summit or flanks, and lead to the release of volcanic gases from the ground and vents.

Question 8

Most useful technique for predicting volcanic activity?

Answer 8

Seismic monitoring

Question 9

What is increased seismic activity associated with?

Answer 9

With eruptions or precursor activity

Question 10

What are pre-eruption ‘quakes, typically?

Answer 10

swarms consisting of dozens to hundreds of events, M < 5, and increasing in frequency or intensity as an eruption is imminent. These ‘quakes occur closer to the eruption location and become shallower as eruption nears.

Question 11

Volcanic eruption ‘quakes are typically sustained with M = ___ to ____ and occur close to the eruption location.

Answer 11

2 – 6

Question 12

How was the onset of activity at Mount St. Helens in March 1980 first noticed? Mount Helens had been inactive for how long before?

Answer 12

initially observed by seismologists who detected both an increased frequency of earthquakes located directly beneath the volcano, as well as a trend to shallower earthquake foci with time. Mount St. Helens was coming to life after over 100 years of quiescence!

Question 13

How to find bodies of magma using seismology?

Answer 13

Earthquake S-waves are not transmitted through liquids, so areas where there are gaps in seismic profiles beneath volcanoes may be interpreted as bodies of magma.

Question 14

What depth do earthquakes at Yellowstone occur frequently? Why do they occur?

Answer 14

depths of <5km. There is a magma chamber 90 km across at a minimum depth of 5km below surface. Earthquakes indicate brittle fracturing of overlying rocks as the magma tries to expand towards the surface.

Question 15

What are acoustic flow monitors? (AFM)

Answer 15

a specialized type of seismometer that are optimized to detect and record high frequency (10 – 250 Hz) vibrations caused by lahars, rather than lower frequency vibrations in the 0.5 – 10 Hz range that are typical of earthquakes

Question 16

Difference between AFM’s and normal seismometers?

Answer 16

AFM’s record higher frequency vibrations caused by lahars. Normal seismometers record lower frequency vibrations caused by earthquakes.

Question 17

Why did Mount St. Helens develop a bulge on its north flank in 1980?

Answer 17

A dome of dacitic magma formed close to the surface, under pressure from volcanic gas trapped inside the existing stratovolcano. This bulge was destroyed during the May 18, 1980 eruption.

Question 18

A volcano changes shape when magma and/or gas moves into a ______ beneath or within the volcanic edifice.

Answer 18

reservoir

Question 19

What are the several ways to measure ground deformation?

Answer 19

Direct measurements of horizontal displacement, tiltmeters, GPS, satellite radar interferometry

Question 20

What is a simple, inexpensive, effective way of measuring ground deformation? What is the downfall of this method?

Answer 20

Direct measurements of horizontal displacement. Can be made by physically taping the distance between two metal stakes, or by measuring an increase in the width of cracks growing on a volcano, and keeping track of the change in distance over time.

Downfall: can be hazardous to field personnel, because they’re physically present within or on an active volcano.

Question 21

What technique did they use on Mount St. Helens from mid-1980 to 1986?

Answer 21

The simple inexpensive method of directly measuring horizontal displacement. Provided info used to predict upcoming eruptions.

Question 22

Geologists at Mount St. Helens measured the increase in ____ between stakes and other markers within the crater, and plotted the increase versus time. In this way they were able to correlate a rapid increase in the _______ between markers with an increased possibility of an eruption. In many instances, these simple measurements accurately predicted dome-growth eruptions within __ hours.

Answer 22

distance ; rate of movement; 24

Question 23

What are tiltmeters?

Answer 23

sensitive instruments that record changes in the tilt of a surface. The change in tilt is measured over time

Question 24

Where do you place tiltmeters?

Answer 24

These instruments are placed around the flanks of a volcano

Question 25

Which volcanoes’ eruptions were successfully predicted with tiltmeters?

Answer 25

Hawaiian shield volcanoes, like Kilauea.

Question 26

Describe how the tiltmeters successfully predicted the Kilauea eruption.

Answer 26

Prior to an eruption, tiltmeters on the broad flanks of Kilauea record inflation of the volcano. Individual tiltmeters record tilting outward from the central crater as the volcano inflates with magma in its interior. After an eruption, the tiltmeters record decreasing tilt as the volcano deflates.

Question 27

How to use GPS to pinpoint horizontal and vertical movement of targets on a volcano?

Answer 27

Through repeated measurements over time. This technique may involve placing automated GPS receivers at known locations around a volcano. Or, geoscientists may make the measurements directly at each site using portable GPS receivers.

Question 28

Complications of GPS?

Answer 28

As is typically the case with monitoring volcanoes, having fixed receivers is safer – less personnel are put in harm’s way. However, expensive equipment can be destroyed by on-going eruptions. Geoscientists must often judge whether to place equipment in dangerous areas, or to visit these areas in times of relative volcanic quiescence to manually take measurements.

Question 29

Safe but expensive way to make ground deformation measurements?

Answer 29

Use InSAR (satellite radar interferometry)

Question 30

What is InSar?

Answer 30

satellite radar interferometry. involves satellites using radar waves to measure the elevation of large areas of the crust in the vicinity of active volcanoes over an interval of time.

Question 31

Where did scientists find a potential magma body approx. 7km deep using InSAR imagery?

Answer 31

in Central Oregon Cascade Range

Question 32

Describe the science of using satellite technology to measure or detect uplifts of the Earth’s surface?

Answer 32

Radio waves are bounced off the surface on two separate passes. Phase differences resolve elevation changes in fractions of the wavelength of the radar.

Question 33

What does increased gas emission possibly mean?

Answer 33

may reflect a change in magma supply rate, a change in the type of magma that is erupting, or a change in the underground fracture system that is routing gas towards the surface

Question 34

. Direct collection of gases emitted at _____ is possible, but in an active volcanic setting this may be getting too close for comfort for most people!

Answer 34

fumaroles

Question 35

What is the correlation spectrometer (COSPEC)?

Answer 35

A COSPEC measures the amount of solar ultraviolet light absorbed by sulfur dioxide and compares it to a standard. The amount of absorption is proportional to the concentration of sulfur dioxide. Measurements are made over a period of time and the data are used to calculate the sulfur dioxide daily emission rate. Allows us to estimate SO_2 emissions in an eruption plume from afar and thus with little danger.

Question 36

What is the FTIR?

Answer 36

Fourier transform infrared spectrometer (FTIR) is a third technique commonly used in sampling and measuring gas emissions from volcanoes. The FTIR analyzes several gases simultaneously and uses a mathematical process (the Fourier transform) to convert the raw data into the desired format, the amount of light absorbed at each wavelength. As in COSPEC, the amount of light absorbed at specific wavelengths indicates the concentration of specific gases in the volcanic plume.

Question 37

Methods for visual observation of volcanoes?

Answer 37

Still photography, video footage, LIDAR images (light detection and ranging)

Question 38

What are still photography and video footage used for?

Answer 38

to document changes to active volcanoes

Question 39

What are LIDAR images used for?

Answer 39

used to calculate the volume of new material added over time

Question 40

What might increased heat flow might indicate?

Answer 40

the presence of new magma at the surface, fracturing of the crust due to magma upwelling, or increased activity at hot springs and/or fumaroles

Question 41

Techniques to measure heat flow?

Answer 41

Direct observations of glowing magma or glowing cracks in volcano.

Aerial remote sensing of infrared spectra to record anomalously hot areas.

Forward looking infrared (FLIR) images taken by planes or satellite to monitor dome growth at Mount St. Helens

Question 42

What kind of data can Remote Sensing (Satellite) Monitoring retrieve?

Answer 42

Temperature

Question 43

What’s an optical pyrometer?

Answer 43

Hand-held device, used to determine the temperature of glowing lava.

Question 44

How do you distinguish volcanic clouds from meteorological clouds?

Answer 44

Volcanic clouds have larger refractive index for silicates.

Question 45

Describe the August 1992 eruption of Mount Spurr.

Answer 45

The August 1992 eruption of Mount Spurr, a stratovolcano in Alaska, was well documented by several monitoring instruments mounted on satellites. (top) Thermal image data from the Advanced Very High Resolution Radiometer (AVHRR) showing the volcanic cloud (dark red areas) 180 minutes after the eruption, about the time of its end.

Dispersal of sulfur dioxide gas released by the eruption as recorded by the Total Ozone Mapping Spectrometer (TOMS) mounted on Nimbus 7, a research-and-development satellite managed by NASA.

Question 46

Level of Concern Colour Code: explain what GREEN, YELLOW, ORANGE, and RED mean?

Answer 46

GREEN: Volcano is in typical background, non-eruptive state
OR, after a change from a higher level,
volcanic activity has ceased and volcano has returned to non-eruptive background state.

YELLOW: Volcano is exhibiting signs of elevated unrest above known background level
OR, after a change from a higher level,
volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

ORANGE: Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain,
OR
eruption is underway with no or minor volcanic-ash emissions (ash-plume height specified, if possible).

RED: Eruption is imminent with significant emission of volcanic ash into the atmosphere likely
OR
eruption is underway or suspected with significant emission of volcanic ash into the atmosphere (ash-plume height specified, if possible).

Question 47

What does a comprehensive volcano monitoring scheme MUST have in order to achieve its goals?

Answer 47

1. installation and upkeep of real-time seismic network
2. installation and upkeep of real-time GPS network
3. gas emission sampling (COSPEC)
4. regular ground measurements (e.g., crack widths)
5. chemical analyses of eruptive deposits
6. daily observations

Question 48

Why is it difficult to predict eruptions?

Answer 48

No one precursor event can predict the exact time of an eruption, especially with enough time to safely evacuate the local populace. More precursors increase the chance of successfully predicting an eruption. But every volcano behaves differently, and any one volcano can change its behavior with time.