Editing Geography of Palau (section)

== Geology ==
The Palau Islands are composed chiefly of accumulated volcanic material and limestone. Geologists distinguish three geologic units of erupted [[volcanic breccia]] and [[interbedded]] [[tuff]]. Weathered material from exposed upper parts of the volcanic islands was eroded away and accumulated in shallow coastal waters forming deposits of clay. The substrata of the volcanic islands are volcanic breccias and tuffs, some flow material, conglomerates, and related sediments. The sediments are extensively lateritic clays and are strongly acid. The [[Airai]] clay deposit covers much of southeastern [[Babeldaob]] Island and exceeds 45 m thick.<ref name=":1">{{Cite book|last=Snyder|first=David.|url=https://catalog.hathitrust.org/Record/003299366|title=Archaeology and historic preservation in Palau|last2=Adams|first2=William Hampton|last3=Butler|first3=Brian M.|date=1997|publisher=U.S. National Park Service|series=Anthropology research series / Division of Cultural Affairs, Republic of Palau 2|location=San Francisco}}</ref>

The rock islands, the platform islands and the eastern half of [[Koror|Oreor]] Island are made up of Palau limestone. The limestone is raised coralline reef structure which formed in the warm tropical waters during Miocene to Pleistocene times. Surrounding the volcanic islands are natural terraced benches resulting from sea level changes and uplifting of the Palau ridge. Two levels of natural terraced benches have been recognized. One bench is 1 m to 2 m above mean sea level, while a second, and much broader, bench is 5 to 10 m above mean sea level. Many villages on Babeldaob Island are built on this second bench. Geologic data indicate that Babeldaob Island has undergone a net uplift of land relative to sea level of about 2 m in the last 4000 years; thus, for most of the Palau coastline, submerged habitation sites in [[Intertidal zone|intertidal]] and coastal [[swamp]] areas are unlikely. Excepting a few [[calcareous]] sand beaches, the rock island edges rise abruptly out of the water, forming steep cliffs. Distinctive geologic features of the rock islands are shear cliffs and a notch cut back into the cliff just above mean sea level.<ref name=":1" />