Transcript Kilauea: The World`s Most Livable Volcano

Kilauea: The World’s Most Livable Volcano
Figure 1: Basaltic lava flows from Kilauea
Kilauea, the most active and intensely
studied shield volcano in the world, is
located on the island of Hawaii (Figure 1).
Shield volcanoes are extremely large
volcanoes composed of layers of basaltic
lava in a gently sloping dome (Figure 2).
Most are volcanic islands, though some are
found on continents as well. Hawaii, the
youngest island in the Hawaiian Island
Chain, is less than a million years old and
fed by a hot spot. A hot spot is an area of
long lived volcanism and high heat flow
from a zone of instability near the coremantle boundary.
As the Pacific plate moved over this
hot spot, successive volcanoes
formed. As seen in Figure 3, the age
of each Hawaiian island indicates when
it was situated over the relatively
stationary hot spot.
More than 50 eruptions have been
witnessed here since record keeping
began in 1823. Most of the activity on
Kilauea during the past 50 years
occurred along the flanks of the
volcano in a region called the East Rift
Zone (Figure 4). A rift eruption here in
1960 engulfed the coastal village of
Kapoho, located nearly 20 mi from its
source. The longest and largest rift
eruption ever recorded on Kilauea
began in 1983 and continues to this
day!
Figure 3: The Hawaiian Island
Chain formed over a hot spot
which produced basaltic
magma from partial melting of
oceanic crust
Figure 2: Anatomy of a shield volcano
Figure 4: Most recent eruptions from
Kilauea occur in the East Rift Zone
A
Because of its lower silica content, basaltic lava
is usually very fluid and flows in thin, broad
sheets or stream-like ribbons. While lavas have
been clocked at 19 mph, flow rates of 30-1000
feet per hour are more common. Two typical
types of Hawaiian flows are aa and pahoehoe
flows. Aa flows have surfaces of rough jagged
blocks with dangerously sharp edges and spiny
projections (Figure 5a). In contrast, pahoehoe
flows exhibit smooth surfaces that often
resemble the twisted braids of ropes (Figure
5b). Pahoehoe means “on which one can
walk.” Hardened basaltic flows commonly
contain tunnels that once were nearly horizontal
tubes carrying lava from the volcanic vent to the
flow’s leading edge. These openings develop
when the interior or a flow remains hot long
after the surface hardens. In these
circumstances, still-molten lava within the tubes
continues its forward motion leaving behind
cave-like voids. Lava tubes allow fluid lavas to
advance great distances from their source
(Figure 6).
B
Figure 5A: Aa lava flows are
characterized by jagged blocks and
sharp edges, while Figure 5b
illustrates the ropey, fluid-like nature
of basaltic pahoehoe flows.
Name: _______________
Kilauea Shield Volcano Questions
1. Define the following terms:
a. Shield volcano: __________________
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b. hot spot: _______________________
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c.
basaltic lava: ___________________
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d. Pahoehoe lava: __________________
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Figure 6: View of an active lava tube as seen
through the collapsed roof
e. aa lava: ________________________
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f. lava tube: ____________________________________________________________________
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2. Why does lava from Kilauea have a low viscosity?
3. Using Bowens Reaction series, what minerals compose basaltic lava?
4. What igneous texture do you expect most of the rocks on Kilauea to have?
5. Compare a composite cone and a shield volcano.