A STUDY OF THE FORMATION MECHANISM OF BEACHROCK IN OKINAWA, JAPAN: TOWARD MAKING ARTIFICIAL ROCK

Beachrock is coastal sediment that has been cemented mainly by calcium carbonate within the intertidal zone in tropical and subtropical regions. Man-made beachrock has the potential to inhibit coastal erosion. Considering this important application, we performed field investigations and laboratory tests to understand the formation mechanism of beachrock in Nago, Okinawa, Japan. We performed a needle penetration test, microbial population count and urease activity test, and conducted elemental and mineral analyses of the beachrock and sand. Some microorganisms at the site showed urease activity and the beachrock cement comprised high Mg calcite (HMC). Our investigation showed that evaporation of seawater and/or urease activity of bacteria may have resulted in precipitation of HMC, leading to formation of the beachrock, with partial solidification of some sandy specimens.