Field Trip - Northern Guam Lens Aquifer Jun 2014 | Page 22

Stop 3: Plumbing of the Aquifer –
Surface and Internal Drainage

Hydrologic role of sinkholes, shafts, and caves

Surface water and sinkhole, Mataguac Hill Peace Memorial Park

Recharging waters enter the aquifer and descend to the water table in two ways: 1) by
slow (months to years) percolation of water from ordinary rainfall that infiltrates through the
ground surface, and 2) by fast flow (minutes to days) of water that ponds in natural surface
depressions (sinkholes) during
heavy storms. The fast flow
process is permanently on display
here in this sinkhole on the flank
of Mataguac Hill, where a small
perennial spring provides a modest
but steady flow of water to the
nearby open cave (see photo on
opposite page) and into the swallow
hole located at the cave’s bottom
(see photo below).

In addition to its significance as a World War II historical
site, the Peace Memorial Park provides an outstanding example
of a natural sinkhole, with a visible active swallow hole at its
bottom. The swallow hole has formed along the contact between
the soluble limestone bedrock above and the insoluble volcanic
basement below. Here, water that constantly flows from the small
nearby spring that forms in the volcanic rock of Mataguac Hill,
and storm waters that occasionally run off the flank of the hill,
enter the aquifer and descend some 400 vertical feet to the water
table.

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