-
Increase in the frequency
of volcanic quakes with rumbling sounds; occurrence of
volcanic tremors
-
Increased steaming
activity; change in color of steam emission from white to
gray due to entrained ash
-
Crater glow due to
presence of magma at or near the crater
-
Ground swells (or
inflation), ground tilt and ground fissuring due to magma
intrusion
-
Localized landslides,
rockfalls and landslides from the summit area not
attributable to heavy rains
-
Noticeable increase in
the extent of drying up of vegetation around the volcano's
upper slopes
-
Increase in the
temperature of hot springs, wells (e.g. Bulusan and Canlaon)
and crater lake (e.g. Taal) near the volcano
-
Noticeable variation in
the chemical content of springs, crater lakes within the
vicinity of the volcano
-
Drying up of
springs/wells around the volcano
-
Development
of new thermal areas and/or reactivation of old ones;appearance
of solfataras.
