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Hibok-Hibok Alert Signals |
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Wednesday, 10 August 2011 09:29 |
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ALERT LEVEL
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CRITERIA
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INTERPRETATION
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No alert
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Background, quiet
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No eruption in foreseeable future
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1
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Low level seismic, fumarolic, other unrest.
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Magmatic, tectonic or hydrothermal disturbance; no eruption imminent.
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2
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Low to moderate level of seismic, other unrest with positive evidence for involvement of magma
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Probable magmatic intrusion; could eventually lead to an eruption.
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3
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Relatively high and increasing unrest, including numerous b-type earthquakes, accelerating ground deformation and rockfalls, increased vigor of fumaroles, gas emission
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Increasing likelihood of an eruption, possibly witin days to week.
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4
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Intense unrest, including harmonic tremor and/or may “long period” (=low frequency) earthquakes or quiet lava emissions and/or dome growth and/or small explosions
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Magma close to or at earth’s surface. Hazardous explosive eruption likely, possible within hours to days
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5
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Hazardous explosive eruption in progress, with pyroclastic flows, surges and/or eruption column rising at least 6 km or 20,000 feet above sea level
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Explosive eruption in progress. Hazards in valleys and downwind
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STAND-DOWN PROCEDURES:
In order to protect against “lull before the storm” phenomena, alert levels will be maintained for the following periods AFTER activity decreases to the next lower level:
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From level 5 to level 4:
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Wait 12 hours after level 5 activity stops
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From level 4 to level 3 to 2:
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Wait 2 weeks after activity drops below level 4
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From level 3 to level 2:
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Wait 2 weeks after activity drops below level 3
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NOTE:
Ashfall will occur from secondary explosions for several years after eruption , whenever rainfall and lahars come in contact with still hot- pyroclastic deposits. These secondary explosions will occur regardless of alert level.
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