Geology Reference
In-Depth Information
broad doming occurring that could be related to mag-
matic movement. Both volcanoes also have seismic
patterns that suggest magma. Both also have hot
springs (but only Yellowstone has numerous geysers;
it also is important to note that many hot springs
around the world are not located in areas with active
volcanoes).
5,000 years that can help predict where the next eruption
might take place? Explain.
10.
Approximately 600 years ago eruptions from the South
Deadman Creek dome included both pyroclastic flows that
traveled about 5 km from the vent, and ash that traveled
about 15 km from the vent. If this dome erupts again, are any
populated areas at risk? If so, which one(s)?
QUESTIONS 4, PART A2
Long Valley
11.
If other vents were to have similar eruptions, could they
place any of the populated areas at risk? Explain.
Figure 4.4 shows the location and timing of recent volcanic
activity in the Long Valley area. The named sites on this map
have all been active in the last 5,000 years. The population of
Lee Vining is approximately 500, the population of June
Lake is somewhat lower, and the population of Mammoth
Lakes is approximately 7,500. There are seasonal variations
in population, however, due to tourism and skiing.
Yellowstone
Although Yellowstone has not had a magmatic eruption for
the past 70,000 years, it is still geologically very active. With
plentiful hot water and substantial heat, Yellowstone is sub-
ject to hydrothermal explosions. With active magma at depth,
Yellowstone also has the potential for renewed, small-scale
volcanic activity. Figure 4.5 is a simplified geologic map of
the park.
12.
Post-caldera viscous rhyolite flows have flowed up to
approximately 10 miles from their vent areas. Refer to
Figure 4.6. If a rhyolitic lava eruption were to occur from a
vent area at the bottom of the canyon, would it likely present
a hazard to developed areas on the canyon rim? Explain.
1.
How many volcanic eruptions (not including steam blasts)
occurred in the past 5,000 years?
2.
What is the average recurrence interval between eruptions
for the past 5,000 years?
3.
How many volcanic eruptions occurred in the past 1,000
years?
13.
How would the hazards be different at Canyon if the
eruption were a pyroclastic flow? Basaltic eruption? Explain.
4.
What is the average recurrence interval between erup-
tions for the past 1,000 years?
14.
Mammoth (near the north edge of the map) is located in
an area of precaldera rocks. There is a series of mapped vol-
canic vents south of Mammoth. Based on the topography of
the area (Figure
4
.5), is Mammoth likely to be at risk if one of
these vent areas erupts a rhyolite flow? A pyroclastic flow? A
basalt flow? Explain.
5.
According to the U.S. Geological Survey (Hill and others,
1998), it has been about 250 years since there was an eruption
at Paoha Island in Mono Lake. Is this area due for an erup-
tion or not? Explain your reasoning.
15.
What if there were new volcanic eruptions in the Old
Faithful area? What kind of eruption(s) could threaten other
developed areas?
6.
How many steam blasts occurred in the past 5,000 years?
7.
a.
What is the geographic relation of steam blasts to the
760,000-year-old caldera?
16.
If a small hydrothermal explosion like Porkchop (Figure 4.7)
were to occur, is the damage likely to be widespread?
b.
What does this relationship imply about the origin of
steam blasts?
17.
What impacts could a 2-mile-diameter hydrothermal explo-
sion have if it occurred in a populated area?
8.
What geologic factors might contribute to there not being
any steam blasts identified that are more than 1,000 years old?
18.
Yellowstone Lake is the large lake on the eastern part of
the caldera (Figure 4.5). What impacts might be expected if a
2-mile-diameter hydrothermal explosion occurred under
the lake?
9.
Is there a trend in the spatial distribution (northern, south-
em, central region, etc.) of volcanic eruptions over the past
