Geology Reference
In-Depth Information
a.
From its profile, is Hawaii most like a basaltic shield vol-
cano, an andesitic composite cone, or a rhyolitic volcano?
b.
Where are the zones of lowest hazard?
b.
What is the vertical exaggeration of your profile? What
would the profile look like with no exaggeration?
c.
What geologic factors might be different between zones
of higher hazard and zones of lower hazard?
c.
Does the amount of vertical exaggeration that you drew
influence your interpretation of the kind of magma in
Hawaii?
d.
Using the information on these two maps, which
town(s) would likely be subject to hazards from the erup-
tion of Pu'u O'o on the east rift zone of Kilauea? (Note
that lava flows downhill.)
Explain.
4.
Look at Figure 4.11b. Analyze it to answer the following
questions.
a.
Where are the zones of highest hazard from Kilauea
and Mauna Loa?
5.
Review hazards listed on Tables 4.1 and 4.2. Lava is not the
only hazard on Hawaii. What other hazards could be
expected in Hilo from an eruption of:
TABLE 4.5 Hazard zones from lava flows on the Island of Hawaii are based chiefly on the location and frequency of
historic and prehistoric eruptions and the topography of the volcanoes. Scientists have prepared a map
that divides the five volcanoes of the Island of Hawaii into zones that are ranked from 1 through 9 based
on the relative likelihood of coverage by lava flows. Caption and table from U.S. Geological Survey
(
http://hvo.wr.usgs.gov/hazards/LavaZonesTable.html
,
downloaded August 4, 2007)
Hazard Zones for Lava Flows on the Island of Hawaii
Percentage of area
covered by lava since
1800
Percentage of area
covered by lava in last
750 years
Zone
Explanation
1
Greater than 25
Greater than 65
Includes the summits and rift zones of Kilauea and
Mauna Loa where vents have been repeatedly active in
historic time.
2
15-25
25-75
Areas adjacent to and downslope of active rift zones.
3
1-5
15-75
Areas gradationally less hazardous than Zone 2 because of
greater distance from recently active vents and/or because
the topography makes it less likely that flows will cover
these areas.
4
About 5
Less than 15
Includes all of Hualalai, where the frequency of eruptions
is lower than on Kilauea and Mauna Loa. Flows typically
cover large areas.
5
None
About 50
Areas currently protected from lava flows by the topogra-
phy of the volcano.
6
None
Very little
Same as Zone 5.
7
None
None
20 percent of this area covered by lava in the last 10,000
yrs.
8
None
None
Only a few percent of this area covered in the past 10,000
yrs.
9
None
None
No eruption in this area for the past 60,000 yrs.
Source: Wright and others, 1992
