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National Volcano Early Warning System*
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Hazard and exposure factors used in threat
assessment of U.S. volcanoes for the National
Volcano Early Warning System.
See appendix text for discussion and explanation
of abbreviations. |
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Hazard Factors |
Score |
Explanation
of Score |
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Volcano type
If volcano type is cinder cone, basaltic field,
small shield, or fissure vents: Score = 0
If volcano type is stratocone, lava domes,
complex volcano, maar or caldera: Score = 1
|
0 |
Easter is primarily made of basaltic lava flows |
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Maximum Volcano Explosivity Index (VEI)
If maximum known VEI ≤ 2: Score = 0
If maximum known VEI = 3 or 4: Score = 1
If maximum known VEI = 5 or 6: Score = 2
If maximum known VEI ≥ 7: Score = 3
If no maximum VEI is listed by GVP and if
volcano type = 0: Score = 0
If no maximum VEI is listed by GVP but volcano
type = 1: Score = 1
If no known Holocene eruptions and the volcano
is not a silicic caldera system: Score =
0 |
0 |
Eruptions resulting in the lava flows evidenced
at Easter would typically have a VEI of 0 or 1,
possibly up to 2. |
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Explosive activity
If explosive activity (VEI ≥ 3) within the last
500 years: Score = 1 |
0 |
No
evidence of this type of activity |
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Major explosive activity
If major explosive activity (VEI ≥ 4) within
last 5000 years: Score = 1 |
0 |
No evidence of this type of activity |
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Eruption recurrence
If eruption interval is 1-99 years: Score = 4
If eruption interval is 100 – 1,000 years: Score
= 3
If eruption interval is 1,000 to several
thousand years: Score =2
If eruption interval is 5,000-10,000 years, or
if no Holocene eruptions but it is a
large-volume restless silicic system that has
erupted in the last 100,000 years: Score = 1
If no known Holocene eruption: Score = 0
|
2 |
Last eruption was ~2,000 years ago, but during
activity it was likely more common.12,
pg. 121 The average would
therefore appear to be 1,000 to several thousand
years. |
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Holocene pyroclastic flows?
If yes: Score = 1 |
0 |
PFs do not occur at the types of volcanoes
constituting the island. |
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Holocene lava flows?
If Holocene lava flows have traveled beyond the
immediate eruption site or flanks and reached
populated areas: Score =1 |
1 |
"...fine-grained banded flows are common in the
vicinity of Hanga-roa."12,
pg. 121 |
|
Holocene lahars?
If Holocene lahars have traveled beyond the
flanks and reached populated areas: Score =1
|
0 |
No mention of lahars anywhere in literature; not
typical of volcanoes seen on Easter |
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Holocene tsunami(s)?
Has it produced a tsunami within the Holocene?
If yes: Score = 1 |
0 |
No mention of tsunami(s) from Easter |
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Hydrothermal explosion potential?
If the volcano has had Holocene phreatic
explosive activity, and/or the volcano has
thermal features that are extensive enough to
pose a potential for explosive activity: Score
=1 |
1 |
Abundance of water made me feel it was
conceivable to cause phreatic eruption should
water mix w/magma beneath surface. |
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Sector collapse potential?
If the volcano has produced a sector collapse in
Quaternary-Holocene time and has re-built
its edifice, or, has high relief, steep
flanks and demonstrated or inferred alteration:
Score = 1 |
0 |
Volcanoes not steep enough. |
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Primary lahar source?
If volcano has a source of permanent water/ice
on edifice, water volume > 106
m3:
Score = 1 |
0 |
No mention of lahars anywhere in literature; not
typical of volcanoes seen on Easter |
Historical Unrest Factors
|
Score
|
Explanation
of Score |
Observed seismic unrest
Since the last eruption, in the absence of
eruptive activity, within 20 km of the volcanic
edifice? If yes: Score = 1 |
0
|
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Observed ground deformation
Since the last eruption, in the absence of
eruptive activity, inflation or other evidence
of magma injection? If yes: Score = 1
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0
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No data for this observation;
presumably not
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Observed fumarolic or magmatic degassing
Since the last eruption, in the absence of
eruptive activity, either heat source or
magmatic gases? If yes: Score = 1 |
0
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No mention, meaning likely not. |
Total of Hazard Factors
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4
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Exposure Factors
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|
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Log10
of Volcano Population Index (VPI)
at 30 km
Calculated with LandScan population database.
Visitor statistics for volcanoes in National
Parks and other destination recreation areas are
added to the VPI factor where available.
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3.579 |
Population ~3,8006,
pg. 169 |
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Log10
of approximate population
downstream or downslope
Population outside the 30 km VPI circle included
within the extent of Holocene flow deposits or
reasonable inundation modeling. This factor to
be used only with volcanoes that have a primary
lahar hazard (e.g. Cascade stratovolcanoes) or
significant lava flow hazard (e.g. Mauna Loa).
|
3.217 |
In my
hazard map I only drew part of Hanga Roa in
lava flow zone; roughly estimated at 1/2
population of island: 1,650 (see reference
above) |
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|
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None |
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Historical evacuations?
If yes, and a permanent population is still
present: Score = 1 |
0 |
None |
Local aviation exposure
If any type volcano is within 50 km of a
jet-service airport, score = 1; if a Type 1
volcano is within 300 km of a jet-service
airport, score = 1; if a Type 1 volcano
is within 300 km of a major international
airport, score = 2; if none of these criteria
are met, score = 0. |
1
|
Easter Island has an airport. |
Regional aviation exposure
This score is based on the log10
of approximate daily passenger
traffic in each region. At present, in the U.S.,
this score ranges from 4 to 5.15. The regional
risk code is applied only to type 1
volcanoes and those type 0 volcanoes that
have produced explosive eruptions. |
0
|
Easter is a type 0 volcano
that appears not to have had explosive
eruptions.
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Power infrastructure
Is there power infrastructure (e.g., power
generation/transmission/distribution for
electricity, oil, or gas) within flowage hazard
zones, or in an area frequently downwind of the
volcano and close enough to considered at some
risk? If yes, score =1 |
1
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Island powered by diesel
generators;21,
pg. 33
assumption made that they may be in hazard zone.
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Transportation infrastructure
Is there transportation infrastructure (e.g.,
port facilities, rail lines, major roads) within
flowage hazard zones, or in an area frequently
downwind of the volcano and close enough to
considered at some risk? If yes, score = 1
|
0
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I made the judgment call that
there are no transportation facilities vital to
the island in danger zones based on aerial
photos.
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Major development or sensitive areas
Are there major developments or sensitive areas
threatened (e.g., National Park facilities,
flood control projects, government facilities,
developed tourist/recreation facilities,
manufacturing or other significant economic
activity)? If yes, score =1 |
1
|
The island contains Rapa Nui
National Park; tourism to see the irreplaceable
moai is the island's main economic
activity.
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Volcano is a significant part of a populated
island
Holocene volcanic deposits cover >25% of land
mass. If yes, score = 1 |
1
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Volcano IS the
populated island!
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Total of Exposure Factors
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10.796
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Sum of all hazard factors x Sum of all exposure
factors = Relative Threat Ranking
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4
x 10.796
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Relative Threat Ranking =
40.796
Overall Threat Score =
Moderate
-Moderate includes volcanoes with
relative threat rankings between 30 and 60
Required Monitoring Level =
Level 3
(Basic Real-time)
-Seismographic monitoring
net
-Deformation monitoring
-Ability to monitor gas emissions
Current Monitoring Status =
Level 1 (Minimal)
-One seismic station on
island
-No evidence of other monitoring effotrs
Monitoring Gap = 2
This analysis implies that the
volcanological situation of Easter Island is under
monitored. This situation likely represents the
fact that Easter has never been active; without a
history of activity or potential activity it is unlikely
that any volcano will be monitored substantially.
Also, from my experience in doing the exercise I think
NVEWS recommends a Level 3 monitoring status less
because of Easter's potential for eruption, and more
because the nature of a small volcanic island forces
critical resources and populations near potential vents.
*This process is from an in
class handout derived
from PDF by John Ewert, USGS
Open-File Report 2005-1164 |
