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Hawai`i Volcanoes National ParkA Restless Paradise

Geology and Monitoring Techniques

Judy McIlrathDepartment of Geology, University of South Florida© 2010 University of South Florida Libraries. All rights reserved.

SSACgnp.QE527.JAM1.7

Core Quantitative Literacy TopicsGraph Interpretation

Supporting Quantitative Literacy TopicsUnit ConversionPythagorean Theorem

Core Geoscience SubjectHot spot volcanismVolcano Monitoring Techniques

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Getting started

After completing this module you should be able to:

•Discuss volcano monitoring techniques

•Calculate surface movement

•Analyze graphs

•Convert measurement units

You should also know where Hawai`i Volcanoes National Park is located and its geologic origin.

Canada

United States

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The setting – Hawai`i Volcanoes National Park

Hawai’i Volcanoes National Park, established in 1916, also holds the designation of an International Biosphere Reserve (1980) and a World Heritage Site (1987). The park is home to two of the world’s most active volcanoes, Kilauea with almost continuous eruptions since 1983 and Mauna Loa, volumetrically, the world’s largest mountain. Far from any plate tectonic boundary, Hawai’i is the youngest island in the Hawaiian island chain which formed as the Pacific Plate moves over a hot spot. Thousands of miles from the closest continent, flora and fauna evolved over the last 70 million years in near complete isolation. Ninety percent of the species found in Hawaii are found nowhere else in the world.

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Evolution of a Hot Spot Island Chain

Ocean crust

Ocean lithosphere

AesthenosphereStationary mantle plume – “Hot Spot”

Lithospheric plate motion

The diagram below shows how ocean island chain “x” evolves through time as the lithospheric plate moves over a stationary hot spot mantle plume in a conveyor belt-type motion.

The Hawaiian Hot Spot

Islands on the map below were created as the Pacific Plate moved over a hot spot. Volcano symbols indicate recent (10,000 years) activity. Loihi Seamount is the youngest volcano and may in time breach the ocean surface and become a new island. Hawai`i has three active volcanoes, Mauna Loa, Kilauea, and Hualalai. Maui has experienced one or two eruptions in the past 1,000 years. Northwestern islands are older and volcanically extinct. Hawaiian Volcano Observatory (HVO), housed within the park, collects seismic, gas, gravity, geochemical, tilt, GPS, and webcam data to monitor the volcanoes.

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Maui

Oahu

Loihi Seamount

Kauai

Monitoring Techniques - Seismicity

Earthquakes are recorded on seismographs when ground motion occurs. Often, harmonic tremor, a continuous rhythmic earthquake, indicates magma movement. Over 100 earthquakes a day are recorded on Hawai`i, most are less than magnitude 3 and cannot be felt by humans.

Question 1. Make observations of the earthquake (1/1/10 to 7/25/10) map of southern Hawaii. Open the Excel template, and write a three-sentence description of your observations. Between what latitudes and longitudes might there be an active volcano?

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Scientist describing seismic monitoring techniques

Seismometer at HVO

Courtesy of HVO/USGS

Hawaii Volcanoes TEMPLATE

Monitoring Techniques - Gas

Question 2: Over what time period were the gas data collected? On what day and in what concentration was SO2 highest? lowest? What units are used to report SO2 emissions?

As magma rises, gases (mainly H2O, CO2, SO2) dissolved in the magma expand and form bubbles due to the decrease in pressure. As the volume of bubbles increases, magma density decreases allowing it to rise higher. If the conduit that the magma is rising through becomes clogged or crusted over, the gases may become trapped, creating a potentially explosive situation (similar to shaking a can of soda). A flyspec (ultraviolet spectrometer) is used to detect the amount of SO2 in the plume. SO2 interacts with sunlight, moisture, and particulates forming volcanic smog (vog) which poses heath risks to humans and animals.

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Gas plume at Halema’uma’u Crater on 7/ 25/2010

Courtesy of HVO/USGS

Monitoring Techniqus - Gravity and Geochemical

Scientists collect samples during eruptions to determine the mineral and gas content of the lava. Lavas low in silica are typically erupted in a non-explosive manner. The table below shows the average chemical composition (weight percent) of rocks from Hawaii and Mt. St. Helens.

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Gravity measurements are used to detect changes in the subsurface as magma moves and fills or drains underground reservoirs. As the magma mass changes in the subsurface, its gravitational attraction at the surface changes as well and is measurable. Gravity measurements are affected by surface deformation, atmospheric pressure, and tidal influences. Therefore, the data collected must be processed to eliminate these external factors. Combined with other monitoring techniques, the corrected data may provide information on subsurface magma or water movement.

Gravimeter Photo courtesy of HVO/USGS

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Monitoring Techniques – Tiltmeters

Tiltmeters placed on the flanks of volcanoes measure inclination of the Earth’s surface. As volume and pressure inside the volcano increase, the volcano inflates causing surface bulges. As magma or gases are released, deflation of the edifice occurs and the surface subsides. Long-term deflation and inflation events (DIs) are detected by tiltmeters that collect data (in microradians) every minute and so are sensitive to surface deformation events. Superimposed on broad deformation cycles are short-term (hours to days) DI events for which the cause is not yet known.

You can simulate a DI event by placing a balloon under a pile of wet sand. Inflate and deflate the balloon to see how the surface deforms! A small level on the sand volcano flank could be a make-shift tiltmeter.

How small is a microradian? If a dime is placed under an I-beam one kilometer in length, the inclination of the I-beam would be one microradian.

In the animation above (click), a volcano emits a small steam and ash plume. With time, additional magma enters the edifice. Increased volume and pressure cause the volcano to inflate. Magma escapes through a vent on the volcano’s flank. Volume and pressure decrease, and the volcano deflates.

inflationdeflation

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Monitoring Techniques – Tilt meters

On a tiltmeter graph, inflation is recorded as an upward trend; deflation a downward trend, with minor episodes along the trend. The graph shows four DI events with a fifth inflation.

deflationInflation

Note the difference in scale on the graph below. What looked like large DI events on the upper graph appear relatively insignificant on the graph below when additional data are added to the time series.

Question 3:For the longer time series, by how many microradians did the edifice inflate overall?

(2010)

(2010)

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Monitoring Techniques – Kinematic GPS & Continuous GPS

Kinematic GPS uses benchmarks placed all over the volcano. Periodically, a scientist hikes to the benchmark and acquires a northing, easting, and up movement. By comparing benchmarks on opposite sides of the crater, determined by the difference in line length between GPS receivers, scientists can get a quick sense of long-term DI events.

Question 4: Using the Pythagorean Theorem, what was the distance between the two points (A, A’) for each of the four data points collected? What was the total change in distance? Write a description of your observations of the differences and similarities between the K-GPS and continuous GPS graphs.

Click here for help with the Pythagorean calculation.

Continuous GPS

Benchmarks and Continuous GPS stations at Puu Oo crater

Line lengths are exaggerated.

GPS receiverGPS receiver

A A’

A

A’

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Monitoring Techniques – Visual Observations and Webcams

Kilauea erupts, mostly quiescently, at the caldera or along the east or southwest rift zones. The Puu Oo cone along the east rift zone has had almost continuous eruptions since 1983.

Click “Enter” to see Puu Oo webcam series from June 17-20, 2007 (Father’s Day event)

Kilauea summit crater in daylight and at night

Click the image above to see a Drainhole piston movie created from a series of webcam images . Go here to see other movies and this one if you are unable to view it here.

Webcams allow scientists to make visual observations without the danger of going to the eruption. Flow maps are used to inform the public of current activity.

Question 5: Go to the Haleamaumau Overlook webcam. What can you see? Write down your observations include the date and time.

Puu Oo lava fountain 1983

2010 Kalapana Flow

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Why monitor Kilauea? # & volume of eruptions

Kilauea rises ~20,000 feet from the ocean floor. The summit crater is 2 ½ miles long and 2 miles wide. The floor of the crater is 400 feet below the rim. Nearly 2,600 acres of lava flows have erupted in the crater since the late 19th century. Near the southern edge of the crater floor is Halemaumau, a pit crater currently emitting a steam and ash plume.

On January 2, 1983, rapid deflation occurred at Kilauea caldera. The east rift zone had elevated earthquake activity, and on January 3, lava erupted along a fissure and centralized at Puu Oo vent, fountaining 1,500 feet above the vent. As fountain activity decreased, lava flows moved toward the ocean engulfing homes in the Royal Gardens subdivision. Flows reached historic Kalapana in 1990.

Question 6: Eruption volumes from 1918 to 2007 for Kilauea are given in cubic yards. Convert the volumes to ft3, m3 and km3. What is the total volume erupted for this time period for each volume unit?

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Why monitor Kilauea? Explosive eruptions

1924 Kilauea Explosion from HVO (courtesy USGS)

Much to the contrary of most Geology textbooks, Kilauea has not always had quiet eruptions. In 1924, the crater floor dropped to a depth of nearly 700 feet. The crater walls became unstable, and rock falls were constant. On May 11, Halemaumau exploded blasting out blocks of rock weighing several tons and emitting an ash plume 20,000 feet into the atmosphere.

Deposits of reticulite, accretionary lapilli, ash, and surge deposits, all created from violent eruptions which occur every few decades to centuries, have been identified. One such deposit (above) can be seen at Hawaiian Volcano Observatory. In 1790, ~80 people in a war party near the summit were killed due to an explosion, making Kilauea the most lethal volcano in the United States. Monitoring Kilauea has tremendously increased the science of volcanology.

Gray layers are ash, accretionary lapilli, and surge deposits and are probably from the 1790 eruption.

The brown layer is reticulite dated to an eruption in the 1500s

Sag bomb – This block was thrown out of the crater and landed on the tephra layer causing it to sag.

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The hazards of an active volcano

Although most eruptions are non-violent, any eruption can cause problems in the following ways:

•Lava flows burn homes and forests.

•Roads can be inundated making areas inaccessible.

•Vog causes respiratory problems in both residents and tourists.

•Tropical plant growing businesses have closed due to the SO2 containing gas plume reaching their growing areas, killing the plants.

•Livestock eat vegetation covered by acids created from the interaction of the gas plume and rain.

•Infrastructure can be damaged. For example, ranchers in the path of the vog can no longer use barbed wire fencing as it rusts away in less than a year.

•Large ash plumes although relatively rare, could pose threats to airplanes.

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End-of-module assignment

1. Hualalai an active volcano on Hawai`i, does not have a webcam. Speculate as to why not.

2. Some of the information regarding eruptions at Kilauea provided in this module is contradictory to what one hears in an introductory geology course. Write a few sentences describing your understanding of a typical Hawaiian volcanic eruption before working through this module and new information that you learned.

3. Go to slide 5, and view the map of the Hawaiian Islands. According to the information presented on slide 4 regarding lithospheric plates moving over a stationary mantle plume hot spot, describe the direction of motion of the Pacific Plate.

4. Using the additional K-GPS data for two stations (B-B’), calculate the distance between the two stations for the five dates provided. Was the distance you calculated the same or different from the data for stations A-A’? Explain.

5. Observe the graph below. Determine the number of DI events recorded on the tiltmeter graph (both short-term and long-term)?

6. Refer to your answer for Question 4. Did the distance between the GPS stations get longer or shorter? Would you infer that the volcano was inflating or deflating during this time period?

(2010)

1983–1986

Pu‘u ‘Ō‘ō(episodic fountains)

1986–1992

Kupaianaha(continuous effusion)

1992–2007

Pu‘u ‘Ō‘ō flank vents(continuous effusion)

2007–present

July 21st, 2007 eruption (continuous effusion)

Kīlauea 1750–1983

Kīlauea 1983-present

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Point 1: Easting = 2, Northing = 10Point 2: Easting = 5, Northing = 20

Kinematic GPS (K-GPS) and the Pythagorean Theorem

The Universal Transverse Mercator (UTM) coordinate system, a grid-based zone method, uses easting and northing coordinate pairs to specify a location at the earth’s surface. The system is similar to latitude and longitude, but calculations in the field are easier with the UTM system as the Pythagorean Theorem can be used rather than difficult trigonometric calculations.

Two example K-GPS coordinates are plotted. The difference in the easting coordinates (∆ x) and the difference in the northing coordinates (∆ y) are two legs of a right triangle. The hypotenuse of the triangle is the distance in meters between the two points.

(∆ x)

(∆ y)

a

bc

Pythagorean Theorem: a2 + b2 = c2

You could make each step in the calculation separately, or you could type the entire formula in one cell:

=((C3-C4)^2+(D3-D4)^2)^(1/2)

Return to slide 11

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