Anieri Morales, ammorale@mtu.edu
Earthquake and volcanic eruption magnitude scales
Objectives
- Providing students information about earthquake and volcanic eruption magnitude
scales
- Understanding the importance of learning about these natural processes and their
effects on humans
Materials needed
- Papers, pencils
- Bag
- Handouts
Time duration
- 50 minutes
Vocabulary
- Earthquake: shaking/trembling caused by the sudden release of energy in the Earth’s
crust
- Seismology: the study of earthquakes
- Seismograph: instrument that detects, records and measures the vibrations (seismic
waves) produced by an earthquake
- Wave amplitude: vertical measurement of the seismic wave from the point hitting
the surface to the highest point of the wave
- Magnitude: amount of energy released by an earthquake at its source
- Ritcher Scale: logarithmic scale that measures magnitude of a seismic wave (used for
moderate, shallow earthquakes)
- Moment Magnitude Scale: quantifies released energy (used for larger magnitude
earthquakes)
- Intensity: Subjective measure of the kind of damage done by an earthquake, as well
as people’s reaction to it
- Modified Mercalli Scale: expresses the intensity of an earthquake’s effects with a
scale from I to XII based on descriptions of damage
- Magma: molten rock material generated within the Earth
- Volcanism: process whereby magma and its associated gases rise through the crust
and are extruded onto the surface or into the atmosphere
-
Volcano: hill or mountain formed around a vent where lava, pyroclastic material and
gases erupt
Effusive eruption: liquid magma emerges quietly to the Earth’s surface
Explosive eruption: escaping gases tear the magma apart into fragments
Volcanic Explosivity Index (VEI): semiquantitative scale for the size of a volcanic
eruption based on evaluation of criteria such as volume of material ejected and
height of eruption cloud.
Introduction/Description
Earthquakes and volcanism are two examples of natural processes/events that are quite
hard to be accurately predicted. For this reason, people should be presented with information
about these processes and events, understand why scientists need to study them, and increase
their awareness of the effects they may have on people. For earthquakes and volcanoes,
scientists use scales to describe the magnitude and intensity of the events. The Richter and the
Moment Magnitude scales are used to determine the magnitude of the earthquake, and the
Modified Mercalli scale is used to describe the intensity of the earthquake. The Volcanic
Explosivity Index is used to describe the size of the volcanic eruption.
Activities
- Lecture the students (10 minutes)
- Asking questions to increase interaction with and between the students (6 minutes)
- “Simulating an earthquake to obtain seismic waves” (6 minutes)
o You will need a paper, a pencil, at least 4 students
o 2 students will shake/lift/move the desk (simulate an earthquake), while 1
student holds a pencil still over the paper (perpendicular to the piece of
paper) and 1 student will slowly pull the paper.
o Students will have created a seismogram
- “Brainstorming: Why should we study earthquakes?” (4 minutes)
- “Mix and match for Earthquakes: Magnitude vs. Intensity and effects” (Use Table 1)
(5 minutes)
- “Experiences with Earthquakes” (2 minutes)
o Briefly describe what was felt during the quake
o How many people felt the quake (“not too many, several, everyone”?)
o Approximate the magnitude and intensity based on the descriptions
- “Brainstorming: Why should we study volcanoes” (4 minutes)
- “Mix and Match for Volcanoes: Size of the eruption” (Use Table 2) (5 minutes)
- “Debate” (8 minutes)
o Evaluate what the students learned by dividing the class in two groups. Put
questions in a bag, let the students pick a question and answer it.
Conclusion
After the lesson, students will have learned how scientists describe the magnitude and
intensity of earthquakes and volcanoes. Students will be able to understand the effects these
events may produce depending on the size of the event.
Assessment/Evaluation
- In order to evaluate the students’ knowledge/understanding of the lecture
presented during that day, the class will be divided in two groups. Questions will be
written in pieces of folded papers and put inside a bag. Students will pick a piece,
read the paper out loud and try to answer the question. Correct answers will get
one point; incorrect answers will give an opportunity to the next person from the
opposing team to answer the question and receive a point. The team with the most
points wins!!!!!
Resources
Magnitude
Earthquake
description
Effects (Intensity)
1-3
Minor
3+
Light
4+
Moderate
5+
Strong
6-7
Major
8+
Extreme
Felt by almost no one.
Felt by very few people.
Tremor noticed by many.
Felt indoors by many.
Felt by nearly everyone. Swaying trees and poles observed.
Felt by all, many people running outdoors. Furniture moved.
Everyone runs outdoors. Poorly built structures considerably
damaged.
Specially designed structures damaged slightly, others collapse.
All buildings considerably damaged. Noticeable cracks on the
ground.
Many structures destroyed. Ground is badly cracked.
Almost all structures fall. Very wide cracks in ground.
Total destruction. Waves seen on ground durfaces.
Table 1: Magnitude vs. Intensity (Richter vs. Mercalli)
(Based on documents from the US Geological Survey)
Table 2: Size of the eruption (Volcanic Explosivity Index)
(Based on documents from the US Geological Survey)
Eruption
Size
0
1
2
3
4
5
6
7
DESCRIPTION
VOLUME OF EJECTED
MATERIAL (m3)
HEIGHT OF THE PLUME
(km)
Effusive
Gentle explosion
Explosive
Severe explosion
Very severe explosion
Violent explosion
Terrific explosion
Super-terrific explosion
Less than 10,000 m3
More than 10,000 m3
More than 1,000,000 m3
More than 10,000,000 m3
More than 100,000,000 m3
More than 1,000,000,000 m3
More than 10,000,000,000 m3
More than 100,000,000,000 m3
Less than 0.1 km
0.1-1 km
1-5 km
3-15 km
10-25 km
More than 25 km
More than 25 km
More than 25 km
Mega-terrific explosion
8
More than 1,000,000,000,000 m3
More than 25 km
MODIFIED MERCALLI SCALE (Source: US Geological Survey)
-
-
-
-
-
-
I. Not felt except by a very few under especially favorable conditions.
II. Felt only by a few persons at rest, especially on upper floors of buildings.
III. Felt quite noticeably by persons indoors, especially on upper floors of buildings.
Many people do not recognize it as an earthquake. Standing motor cars may rock
slightly. Vibrations similar to the passing of a truck. Duration estimated.
IV. Felt indoors by many, outdoors by few during the day. At night, some awakened.
Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy
truck striking building. Standing motor cars rocked noticeably.
V. Felt by nearly everyone; many awakened. Some dishes, windows broken.
Unstable objects overturned. Pendulum clocks may stop.
VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of
fallen plaster. Damage slight.
VII. Damage negligible in buildings of good design and construction; slight to
moderate in well-built ordinary structures; considerable damage in poorly built or
badly designed structures; some chimneys broken.
VIII. Damage slight in specially designed structures; considerable damage in ordinary
substantial buildings with partial collapse. Damage great in poorly built structures.
Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture
overturned.
IX. Damage considerable in specially designed structures; well-designed frame
structures thrown out of plumb. Damage great in substantial buildings, with partial
collapse. Buildings shifted off foundations.
X. Some well-built wooden structures destroyed; most masonry and frame
structures destroyed with foundations. Rails bent.
XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent
greatly.
XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air.
How I will teach the students…
Starting the class:
I will introduce myself to the class: my name, graduate student at Michigan Tech in Geology
Dept., my purpose with the students in the class room: briefly explaining what earthquakes and
volcanoes are and how scientist obtain their magnitude scale.
Questions for the student:
-
I believe you guys and girls received some background information during the last
weeks about earthquakes and volcanoes, so I would like someone to define what is
an earthquake, where would you expect for earthquakes to occur? (Hint: plate
tectonic boundaries, fault zones)
o I will write the answers received on the board
-
I will ask the same questions for volcanoes: what are volcanoes? Where would you
expect to find a volcano? (Hint: plate tectonic boundaries) What types of volcanoes
are there (effusive vs. explosive)
o I will write the answers received on the board
-
Find similarities between them (Some earthquakes are related to volcanism)
-
Start with Earthquake material
-
Earhquake:
o Shaking or trembling caused by the sudden release of energy in the Earth’s
crust
o This energy is released in the form of waves (seismic waves) that travel
through the intertior and through the surface of the earth.
-
Seismology:
o The study of earthquakes
o Receive these waves on an instrument called the seismograph
o Scientists then measure the amplitude of this waves (from point hitting the
surface to the highest point) to obtain the magnitude of the earthquake
-
Magnitude:
o Total amount of energy released by an earthquake at its source
o Magnitude is determined measuring the amplitude of the largest seismic
wave recorded. To avoid large numbers, the results were converted to a
numeric magnitude value (Example: Magnitude 6 earthquake’s amplitude is
10 times more than that produced by a 5, 100 times more than that
produced by a 4, 1000 times more than that produced by a 3…)
-
Activity: “Simulating an earthquake to obtain seismic waves”
o How would you measure the magnitude of the wave using your seismogram?
-
Make a comment: Some people may think, why should we know this information?
Why is this important for me? Ask the students: Why should we study earthquakes?
(Hint: expected answers: Earthquakes are destructive, they cause many deaths and
injuries to people, affect economies of countries with cleanup costs, lost of jobs,
structure damages… If you don’t leave on these areas, you may travel to one of this
areas where there is a threat of earthquakes and you should know what to do if you
experience one)
-
Activity: “Brainstorming: Why should we study earthquakes?”
-
Activity: “Mix and match for Earthquakes: Magnitude vs. Intensity and effects” (Use
Table 1)
-
Describe what the Richter and Mercalli scales are (Give out handouts)
o Richter Scale

Open-ended scale that measures the amount of energy released
during an earthquake (measures magnitude)
o Moment Magnitude Scale

Modification of the Ritcher Scale used for larger magnitude
earthquakes

Considers the area of a fault along which rupture occurred and the
amount of movement of rocks adjacent to the fault
o Modified Mercalli Scale

Scale used to characterize earthquake intensity based on damage

Intensity

Subjective measure of the kind of damage done by an
earthquake, as well as people’s reaction to it
-
Activity: Ask the students if they have ever felt an earthquake. If someone says yes,
tell the student to briefly describe what he felt, observed, heard, etc. If not, I’ll give
an example. Based on the descriptions, let the students approximate the intensity
and magnitude of the event
-
Facts to know:
o Largest earthquake of the century in the world: Chile 1960, 9.5 magnitude
o Largest earthquake of the century in the US: Alaska 1964, 9.2 magnitude
Done with earthquakes… now, volcanoes!
-
Start the volcano material
-
Magma:
o Molten rock material generated within the Earth
-
Volcanism:
o Process whereby magma and its associated gases rise through the crust and
are extruded onto the surface or into the atmosphere (eruptions)
-
Volcano:
o Hill or mountain formed around a vent where lava, pyroclastic material and
gases erupt
-
Three main types of volcanoes (differ in composition, shapes, activity):
o Shield volcanoes (Large volcano; low, rounded profiles with gentle slopes
ranging from 2 to 10 degrees. Formed by lava flows)
o Cinder Cones (small volcano; steep-sided, explosive liquid lava and ash)
o Composite/Stratovolcanoes (Large volcano; explosive viscous lava,
pyroclastic fragments, mudflows)
-
Draw the volcanoes on the board
-
Ask the students if they know the two major type of volcanic eruptions (Hint:
effusive vs. explosive)
-
Ask the students to give an example of effusive eruption (Hawaii: liquid magma
emerges quietly at the earth’s surface to form a lava flow or dome) and explosive
eruption (Pinatubo: escaping gases tear the magma apart into fragments).
-
Cause of explosive activity: Explain how the build-up of gas pressure causes eruption
of explosive volcanoes, pressure comes from heating of dissolved gases in the
magma.
-
ACTIVITY: “Brainstorming: Why should we study volcanoes”
-
It is because of these dangers presented by earthquakes and volcanoes that scientist
need to study them. So people could plan and be prepared for these events.
-
Activity: “Mix and Match for Volcanoes: Size of the eruption” (Use Table 2)
Talking about how scientists measure the magnitude scale
-
Explain Volcanic Explosivity Index:
o Volcanic Explosivity Index (VEI)
-

Semiquantitative scale for the size of a volcanic eruption based on
evaluation of such criteria as volume of material explosively ejected
and height of eruption cloud

Take a look at VEI table in handout

Discuss the table (range of numbers, volume of ejected material,
eruption column height, eruptive style/type, duration of continuous
blast)

Fatalitites, injuries and damages are not included (not part of VEI,
more like destructiveness index)
FINAL ACTIVITY: Debate!! Divide the class in two groups, put folded papers with
questions inside a bag… the group with the most points wins!!!