CAVE RESEARCH AND PARK SERVICE UNITS IN THE MARIANA ISLANDS

A unique public cave and karst lands area is the Mariana Islands of the western Pacific. The War in the Pacific National Park Service (NPS) unit on Guam, the American Memorial Park NPS unit on Saipan, and the proposed NPS North Field Historic District on Tinian all operate on carbonate islands. Under the Carbonate Island Karst Model (CIKM), these islands fall into the Composite and Complex categories, where eogenetic limestones and weathered volcanics are exposed on the surface. Precipitation is autogenic on the limestones, which also capture allogenic flow from the adjacent volcanics. Conduit flow from allogenic inputs produces epigenic caves while freshwater/saltwater mixing produces hypogenic caves in parallel and sometimes overlapping environments. Epigenic conduits, and flank margin caves, can both distort the fresh-water lens; structure and basement/carbonate relationships can add to that distortion, making prediction of lens position and volumes difficult. Contamination is possible from both non-point and point sources. Water resource management is both a quantity and quality issue.

Karst form and distribution greatly affected the nature and progress of the WWII conflict on these islands. On the limestone outcrops, surface water is absent and most caves are oriented along the location of former fresh-water lens positions, such that the only fresh water they contain is from vadose percolation. For soldiers on both sides of the conflict, the water resources were a constant problem, and many caves contain calcite-coated containers of various forms used to gather water. The distribution of hundreds of flank margin caves at various paleo-lens positions created natural defensive bastions which were extensively exploited by the Japanese. Epigenic stream caves, abandoned phreatic lift tubes, and fissure caves were also utilized. Tunnels and concrete were used to integrate these caves into effective defense networks with interlocking fields of fire. The lessons learned about cave use by the Japanese in the defense of the Mariana Islands was utilized later in the war on volcanic islands such as Iwo Jima, where all “caves” were artificial. The caves of the Marianas today contain numerous military remains, including dangerous unexploded ordinance.