The danger from lahars around Mount Pinatubo
didn't end when the eruptions did. Ash deposits
are eventually covered by vegetation and compacted
into rock. However, while the ash is loose, it
can be remobilized and move downhill every time
it rains. The lowland areas surrounding Mount
Pinatubo remained vulnerable to deadly lahars
sweeping down mountain valleys for years after
In an attempt to keep lahars from overflowing
riverbanks and covering cities and farmlands,
earthen dikes were built along some riverbeds.
These efforts to save land and homes weren't always
effective, however. Large areas of farmland were
covered by lahars and can no longer be farmed.