Laboratory Manual for Introductory Geology 4e

EXERCISE 5.15
Stratovolcano Disaster Case Histories (continued )
Name:
Course:
Section:
Date:
False-color satellite image showing Vesuvius and the Naples metropolitan
area (outlined in white).
Vesuvius
0 5 10 miles
0 5 10 km
II. Cascade Range, western North America [VEI 3–7]: The Cascade Range is a chain of stratovolcanoes that extends
from northern California to southern British Columbia. The range is being formed by the subduction of a small plate within
the Pacific Ocean (the Juan de Fuca Plate) beneath North America. Its prominent peaks include Mts. Rainier, Baker, Hood,
Shasta, Lassen (VEI 5 3), and St. Helens (VEI 5 5), as well as Mt. Mazama, the apparently extinct stratovolcano whose
eruption produced what is now Crater Lake (VEI 5 7).
Mt. St. Helens has been by far the most active of these peaks, and it and Mt. Lassen are the only peaks to have erupted
since 1900. In 2004, 24 years after its explosive 1980 eruption, Mount St. Helens erupted again, this time quietly, exuding
mostly viscous lava. In 2017, around the anniversary of the 1980 eruption, geologists detected several swarms of small
earthquakes beneath the mountain, similar to those that had preceded that eruption. Preliminary analysis suggests that
the earthquakes indicate magma rising from depth, but an imminent eruption is not anticipated.
Locations of major Cascade Range stratovolcanoes and their eruptive
histories over the past 4,000 years.
Eruptive history of Mt. St. Helens since
1400 c.e.
Pacific Ocean
Wash.
Oreg.
Calif.
Baker
Glacier Pk.
Rainier
St. Helens
Adams
Hood
Jefferson
Three Sisters
Newberry
Crater Lake
Medicine Lake
Shasta
Lassen
4000 2000
Years ago
0
200
2000
1900
1800
1700
1600
1500
Dome eruption
Ash fall 1 nuée ardente 1 lahars
Dormant interval
Dome eruptions 1 ash falls 1 lava
Ash falls 1 lahars
Dormant interval
Nuée ardente
Dome eruption 1 lahars
Dormant interval
Ash falls 1 nuée ardente
1400
Nuée ardente
(continued)
138 CHAPTER 5 USING IGNEOUS ROCKS TO INTERPRET EARTH HISTORY