Report Number: 96
Year: 2002

Karst Geology and Hydrology of Tinian and Rota (Luta), CNMI: a Preliminary Report

The karst geology and hydrology of Tinian and Rota (Luta), CNMI, are being inventoried and studied in detail for the first time. The work described in this report includes photodocumentation, field survey and mapping, and classification of karst features, in order to characterize karst development and its implications for the aquifer properties of the carbonate units on these islands. Previous work on carbonate islands in the Bahamas, Atlantic, and Mariana Islands (Guam and Saipan), has been used to develop the Carbonate Island Karst Model (CKIM), a conceptual model that describes the fundamental geologic features, including structural and lithologic controls, that control water movement and karst development in eogenetic rock of carbonate islands. This model is being further developed and applied to the karst geology of Tinian and Rota. Karst features have been classified into four general categories, which reflect the karst features that capture, store, transport, and discharge fresh water in the limestone aquifer: epikarst, closed depressions, caves, and discharge features. Tinian and Rota utilize different means for producing potable water from their karst aquifers, each of which presents water managers with unique opportunities and challenges. Tinian utilizes shallow, Maui-type wells to skim water from the top of the freshwater lens aquifer for public use, while Rota relies entirely on natural discharge captured from cave springs at 350 meters elevation. Future research priorities are presented, which include the continuation of the karst inventory, the implementation of a structural inventory, the detailed geologic mapping of limestone/volcanic contacts in order to locate parabasal water, the implementation of long-term meteorological studies, and intense local groundwater investigations (dye traces). This report thus provides basic information for directing continued research on the islands of Tinian and Rota toward lines of inquiry that will provide water managers with an accurate understanding of the unique characteristics of the islands' karst aquifers. Such understanding is the first prerequisite for developing and implementing effective and reliable water management plans.

Kevin W. Stafford
John E. Mylroie
John W. Jenson