Unit 10 Earth Science
Chapter 29 Formation of Rocks
Name____________________________________
Lab 29.1 Volcanoes
In this investigation, you will learn how volcanoes are associated with plate boundaries, and you will
learn how volcanic eruptions are related to magma chemistry.
All active volcanoes erupt and release material that is very hot and therefore dangerous. But some
volcanoes are especially dangerous because of the sudden, violently explosive nature of their eruptions.
Less explosive volcanoes spew lava fountains and streams of melted rock, but in a gentle manner. In
this investigation, you will discover key differences between gentle and explosive volcanoes and will
discover a pattern in their geographic distribution.
Plume height
Magma
Part 1—The Volcanic Explosivity Index
Geologists have developed a number scale that is used to describe volcanic eruptions. This number
scale is called the Volcanic Explosivity Index, or VEI. The higher the VEI, the more explosive or violent
the eruption of a volcano. Explosive eruptions are associated with high plume of lave and ash escaping
from the top of the volcano. Volcanoes with low VEI numbers have gentle eruptions. The plumes of
these eruptions are not very high and not as much lava is released when the volcano erupts. The table
on the next page provides a list of examples of volcanoes and their VEI ratings.
Unit 10 Earth Science
Chapter 29 Formation of Rocks
Examples of volcanoes and VEI ratings
VEI Plume Height
Volume (m3)
0
1
2
3
4
5
6
7
8
< 100 m
100-1000 m
1-5 km
3-15 km
10-25 km
> 25 km
> 25 km
> 25 km
> 25 km
1.
≥ 1000
≥ 10,000
≥ 1,000,000
≥ 10,000,000
≥ 100,000,000
≥ 1,000,000,000
≥ 10,000,000,000
≥ 100,000,000,000
≥ 1,000,000,000,000
Average time interval
between eruptions
one day
one day
one week
one year
≥ 10 years
≥ 100 years
≥ 100 years
≥ 1,000 years
≥ 10,000 years
Example
Kilauea
Stromboli
Galeras, 1992
Ruiz, 1985
Galunggung, 1982
Mount St. Helens, 1981
Krakatoa, 1883
Tambora, 1815
Toba, 71,000 years ago
What characteristics of a volcano might increase the plume height?
2. Would it be possible to have eruptions with a VEI of 7 in the same year?
Part 2—Finding a pattern of volcanoes
1. The table on the next page provides the position by latitude (Lat) and longitude (Long) for eight
volcanoes represented by two-letter symbols. The left-hand group is known to erupt violently.
The right-hand group is known as gentle or less violent.
2. Plot the locations of all volcanoes on your bathymetric map. Lines of latitude are horizontal;
they are described as being either north (N) or south (S) of the equator. Lines of longitude are
vertical; they are described as being east (E) or west (W) of the prime meridian at 0° longitude.
3. Represent each volcano with its two-letter symbol. Represent violent volcanoes with a red
marker and gentle volcanoes with a blue marker.
Unit 10 Earth Science
Chapter 29 Formation of Rocks
PN
KR
KA
BE
Violent Volcanoes
Lat 15.1°N, Long 120.4°E
Lat 16.7°S, Long 105.4°E
Lat 58.3°N, Long 155.0°W
Lat 56.1°N, Long 160.7°E
MA
FE
ER
PT
Gentle (less violent) Volcanoes
Lat 19.5°N, Long 155.5°W
Lat 0.4°S, Long 91.6°W
Lat 13.6°N, Long 40.7°E
Lat 21.2°S, Long 55.7°E
4. How do the locations of the two kinds of volcanoes relate to the locations of plate boundaries?
5. What is the relationship between the nature of a volcanic eruption and plate boundary
features?
Part 3—Magma Chemistry
The table below provides information about the magma chemistry of certain volcanoes. Study the table
and think about how magma chemistry relates to a volcano’s location. Then, answer the questions that
follow.
Volcano
Pinatubo (PN)
Krakatoa (KR)
Katmai (KA)
Bezymianny (BE)
Mauna Loa (MA)
Fernandina (FE)
Erta Ale (ER)
Piton de la Fournaise (PT)
1.
Type
stratovolcano
stratovolcano
complex stratovolcano
complex stratovolcano
shield
shield
shield
shield
VEI
6
7
3
2
0
2
2
1
Magma Chemistry
Magma Type
Silica
rhyolite
high
rhyolite/andesite
high
andesite
moderate
andesite
moderate
basalt
low
basalt
low
basalt
low
basalt
low
Water
high
high
high
high
low
low
low
low
How does magma chemistry differ between violent and gentle volcanoes? How does the
chemistry of magma cause an explosive eruption?
2. Does magma chemistry seem to be related to the location of the volcano? Explain your answer.
Unit 10 Earth Science
Chapter 29 Formation of Rocks
3. What information would you need to know about a volcano to be able to predict the type of
eruption it may have?
a. What characteristics lead to gentle eruptions?
b. What characteristics lead to explosive eruptions?