The echinoderms are important both ecologically and geologically. Belum Caves are geologically and historically important caves. These may represent tectonic activity, which would indicate that Xanadu is geologically young. Echinoderms are important both biologically and geologically. The Pacific Northwest volcanoes continue to be a geologically active area. Some areas contain no craters, indicating major resurfacing events in the geologically recent past. Belum Caves are geologically and historically important caves in the district. Living fossils exhibit stasis over geologically long time scales. The region is geologically active with landslides and earthquakes. Due to the low rainfall and geologically recent eruptions, its soil consists mostly of clinker. The Lesser Sunda Islands consist of two geologically distinct archipelagos. The Florida caves are formed from geologically young limestone with moderate porosity. There are two geologically distinct plains regions on Mercury. Moldova's hills are part of the Moldavian Plateau, which geologically originate from the Carpathian Mountains. Indonesia is a geologically unstable country.