Geology Reference
In-Depth Information
TABLE 4.4 Volcanic Hazards and Their Relative Risks at Mt. Rainier, During Eruptions and in Dormant Periods
Risk Close to
Mt. Rainier
Risk Away from
Mt. Rainier
Risk During
an Eruption
Risk in Dormant
Periods
Hazard
Lava flow
Phreatic (steam-or gas-driven)
eruptions
Volcanic bombs
Tephra
Pyroclastic flows
Lahars
Jokulhlaups (glacier-burst
floods)
Collapse of part of upper
cone
Debris avalanche
Volcanic earthquakes
Gases
b.
Assume that there are about 30 minutes from the time a
lahar starts on the upper slopes of Mt. Rainier until it
reaches Orting. Where do you suggest citizens of Orting
go? Explain your choice.
Hawaii
Figure 4.11a is a map of the Island of Hawaii, and
shows general zones of volcanic hazards. It also identi-
fies the five major volcanoes that compose the island.
Table 4.5 describes how the U.S. Geological Survey has
identified nine different levels of hazards on the
island. Figure 4.11b is a more detailed map of lava flow
hazards from Kilauea volcano.
c. In 1990, the population of Orting was about 2,100 peo-
ple. In 2005 it was approximately 4,500 people. What addi-
tional risks are created by population growth in Orting?
QUESTIONS 4, PART C
1.
Use the data in Table 4.5 and Figures 4.11a and b. Is the
hazard from lava flows greater in the northern or southern
part of the island of Hawaii?
PART C. SHIELD VOLCANOES
Shield volcanoes are characterized by the eruption of
basaltic magmas, which have low viscosity and there-
fore cannot develop steep sides to their edifices.
Basaltic eruptions, despite their drama, are the least
explosive types of eruptions. In Hawaii, shield volca-
noes typically erupt either from central vent areas or
from rift zones that extend laterally from the central
vents for many kilometers.
2.
Is anywhere on the island completely safe from volcanic
hazards? Explain.
3.
Use topographic data on Figure 4.11a and sketch on lined
or graph paper a topographic profile from the City of Hilo
through the summit of Mauna Loa to the ocean on the west.
(See Exercise 2 for information about drawing topographic
profiles.)
