Activity 2 Volcanoes-2 (1)
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GEOL 101: ACTIVITY 2—VOLCANOES
PART A: Monitoring Volcanoes & Communicating Risks: Yellowstone Kaatje van der Hoeven Kraft (Whatcom Community College) and Rachel Teasdale (California State University Chico)
Read the following to answer the accompanying questions:
Mean Recurrence Interval
Geologic events happen over very long time spans and occur somewhat randomly. While they are based on systems that occur consistently (e.g., slow gradual movement of plates results in a release of that stress as an earthquake), there is not a specific time that it should occur or will occur. In order to better understand this randomness, we determine a recurrence interval (or mean recurrence interval) to represent the average time between events. Volcanoes are one geologic event for which determining a mean recurrence interval can be helpful to better understand the range of activity, particularly for volcanoes that erupt very infrequently, like Yellowstone Caldera (Figure 1). Over the last 2.1 million years, there have been three major eruptions at Yellowstone, resulting in a Mean Recurrence Interval (MRI) of 600,00-800,000 years. Figure 1. The past three eruptions for Yellowstone Caldera occurred 2.1 million, 1.2 and 640,000 years ago. Image Credit: USGS
In order to better understand MRI’s and how they can be useful at a range of time scales for assessing and monitoring volcanic activity, you’ll be calculating MRI’s in earthquake activity in Yellowstone and volcanic eruption MRIs for other major volcanoes. To prepare you, work through the sample problems below.
Calculating Mean Recurrence Intervals
The formula for calculating a very basic recurrence interval is:
T = N/n
Where T
is the recurrence interval, N
is the number of years on record (how long back do we have information for events occurring in this region), n
is the number of events on record.
Example
So with three extremely large explosive eruptions at Yellowstone in the last 2.1 million years, we
can calculate:
T
= 2.1 million years/3 events = 700,000 years/event
USGS reports that Yellowstone’s MRI is more broadly 600,000-800,000 years. The last large explosive eruption was 640,000 years ago, but smaller eruptions have occurred since then. It should be noted, that just because there was an eruption 50,000 years ago, does not mean that it will be another 650,000 years before the next eruption. Because major eruptions do not occur regularly, we try to understand their frequencies by examining the probabilities of their occurrence. Your turn
Use the data in Table 1 to determine the MRIs for the following volcanoes.
Volcano Name
Years since oldest known eruption (N)
# of Confirmed Events since oldest known eruption (n)
MRI (T)
Mt. Baker
Lassen Peak
Table 1: Data to calculate MRI. Data is from the Smithsonian Institution’s Global Volcanism Program: https://volcano.si.edu/
Mt. Baker
1880
1870
1863
1859
1858
1954
1852
1843
1820
Lassen Volcanic
Center
1914
1666
980
880
800
Seismic Swarms
A seismic swarm occurs when there is an unusually large number of minor earthquakes relative to what is considered to be “background” seismic activity. Background seismic activity may be
occurring regularly in small amounts. A swarm is distinguished by seeing a large number in these small events in a shortened period of time. Many active volcanoes have seismic swarms that may or may not be related to eruptive activity. An active volcano is one because magma is moving and generating seismic waves in the process.
Movement does not always equate to activity. Use the graph below (Figure 1) to answer the following questions to turn in:
1.
Describe the axes of this graph and what it illustrates in your own words.
2.
Circle (or name the date ranges for) the three
most important seismic swarms in the year 2017 at Mount St. Helens.
3.
How did you determine what constituted a seismic swarm? 4.
What information do you have, what information is missing? What information/data would you like to know? Note that MRIs for earthquake swarms can also be calculated!
Figure 1: Number of earthquakes per day at Mount St. Helens in 2017. Data from USGS.
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PART B: Volcanic Monitoring
I: Assessing Areas at Risk
Volcanoes erupt every day, but we do not hear about volcanic disasters every day. Let’s first assess what makes a volcano dangerous. Navigate to www.volcano.si.edu
1.
How many currently active volcanoes are there around the world? (Found under “New Activity/Highlights”). If you click on “current eruptions,” you will see that many of these volcanoes have been active for many many years.
2.
When did the Nevado del Ruiz volcano begin erupting during its most recent string of eruptions? What is VEI? What is the maximum VEI of this most recent string of eruptions? Now at the top, mouse over “Database,” and click the fourth item down “volcano search.” We will investigate the Mt. Vesuvius volcano that destroyed the cities of Pompeii and Herculaneum in 79 AD. In the volcano name box, type Vesuvius
. Click on the link that comes up. 3.
Under “General Information” you will find details about the volcano type, tectonic setting, geology, and population living near the volcano. How many people live within:
5km?
10km?
30km?
100km?
4.
Now click on the “eruptive history” tab. The Holocene is the current geologic epoch
which began ~11,500 years ago. How many known eruptive events have occurred at Mt. Vesuvius during this time? (Hint, you do not need to count them; it is listed at the top of the table.)
5.
Calculate the mean recurrence interval (MRI) of all volcanic eruptions at Mt. Vesuvius.
6.
What was the volcanic explosivity index (VEI) of the 79 AD eruption? Calculate the MRI
for this size eruption at Mt Vesuvius?
7.
The Sheveluch volcano in Russia is one of the most active volcanoes in the world. Its current eruption max. VEI is 4, and it has been active since August of 1999. However, no
one lives within 30 km of the volcano, and only 1,700 people live within 50 km. How much of a hazard is this volcano compared to Mt. Vesuvius?
II: Monitoring Volcanoes Example: Yellowstone Part 2 was developed after an activity by Rachel Teasdale (California State University Chico) and Kaatje van der Hoeven Kraft (Whatcom Community College).
i. Seismic data at Yellowstone
There are three decades worth of data at the end of this file. 1990–1999
2000–2009
2010–2018
Divide up the three decades among your group members.
Then, on the table below:
1.
Identify the number of seismic swarms that occurred
during each decade, and indicate when the seismic
swarm(s) occurred during each decade.
2.
Indicate the duration of the swarm(s).
3.
Calculate the MRI of seismic swarms for the Yellowstone Caldera from the full class data set.
Figure 1 Yellowstone caldera (red line and GPS station locations (red triangles). Map from USGS
Decade
Date(s) of swarms
Duration of swarm(s)
1990-
1999
2000-
2009
2010-
2018
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ii. Assessing the State of Yellowstone
Analyze the GPS data for the most recent decade (January 2010 to now) for land surface changes
near Norris Geyser Basin in Yellowstone.
4.
The GPS data above show vertical changes in the land surface near Norris Geyser Basin. Inflation and deflation of the group surface is linked with magma movement underground, but it is not necessarily linked with eruption. How many inflation events have occurred at Yellowstone since 2004?
5.
Do all earthquake swarms relate to an inflation/deflation event?
6.
Are there reasons for EQ swarms without magma movement? 7.
Imagine you work as a geologist at Yellowstone. A concerned citizen hears on the news that earthquake activity in the park has been elevated for a few months. They heard from their friend on social media that earthquakes near other volcanoes preceded major volcanic eruptions, and their friend specifically cited the earthquake preceding the eruption of Mt. St. Helen’s in 1980. How might you respond to this concerned citizen?
Data For Part B exercise II . i.
: Data source: http://quake.utah.edu/regional-info/earthquake-catalogs
Direct download: http://quake.utah.edu/wp-content/uploads/Yell_1982_2018Q1.csv
Earthquake data for the last three decades in Yellowstone National Park
1/4
/19
90
5/1
2/1
990
9/17/1990
1/23/1991
5/3
1/1
991
10/6/1
991
2/11/1992
6/18/1992
10/24/1992
3/1/1993
7/7
/19
93
11/12/1993
3/2
0/1
994
7/26/1994
12/1/1994
4/8/1995
8/1
4/1
995
12/20/1995
4/26/1996
9/1/1996
1/7/1997
5/15/1997
9/2
0/1
997
1/2
6/1
998
6/3
/19
98
10/9/1998
2/1
4/1
999
6/2
2/1
999
10/28/1999
0
50
100
150
200
250
300
350
400
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
Earthquakes in Yellowstone: 1990-1999
Number of located earthquakes per day
Cumulative count
Date
Earthquakes per day
Cumulative number of earthquakes
1/4/2000
5/11/2000
9/16/2000
1/2
2/2
001
5/3
0/2
001
10/5/2
001
2/1
0/2
002
6/18/2002
10/24/2002
3/1
/20
03
7/7
/20
03
11/12/2003
3/1
9/2
004
7/2
5/2
004
11/30/2004
4/7
/20
05
8/13/2005
12/19/2005
4/26/2006
9/1/2006
1/7
/20
07
5/1
5/2
007
9/2
0/2
007
1/26/2008
6/2/2008
10/8/2008
2/13/2009
6/2
1/2
009
10/27/2009
0
50
100
150
200
250
300
350
400
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
Earthquakes in Yellowstone: 2000-2009
Number of located earthquakes per day
Cumulative count
Date
Number of Earthquakes per day
Cumulative number of earthquakes
1/3/2010
4/1
8/2
010
8/1
/20
10
11/14/2010
2/27/2011
6/1
2/2
011
9/25/2011
1/8/2012
4/22/2012
8/5/2012
11/18/2012
3/3/2013
6/16/2013
9/2
9/2
013
1/12/2014
4/2
7/2
014
8/10/2014
11/23/2014
3/8
/20
15
6/2
1/2
015
10/4/2015
1/1
7/2
016
5/1
/20
16
8/1
4/2
016
11/27/2016
3/1
2/2
017
6/25/2017
10/8/2
017
1/21/2018
0
50
100
150
200
250
300
350
400
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
Earthquakes in Yellowstone: 2010-2018
Number of located earthquakes per day
Cumulative count
Date
Number of earthquakes per day
Cumulative number of earthquakes
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