The geologic and natural history of the present island of Kauai (age greater than 5.1 million years) represents only 0.11% of the time since the origin of the Earth about 4.6 billion years ago. Human history extends to 4-5 million years ago (about the time of the first hominids). The archaeological, anthropological and Hawaiian cultural histories on Kauai occupy only the last 2,000 years, or only about 0.04% of the age of the island. Polynesian and Hawaiian oral history on the island extends to the time of the first occupants. Their written history encompasses less than 220 years, since the time of the first significant contact by Europeans.
The early inhabitants of the isolated volcanic islands of Hawaii were limited in terms of available natural earth materials. Although displaying an advanced culture in terms of language, social structure, craftsmanship and navigational skills, they possessed only stone-age implements at the time of European contact. Hawaiian volcanic rocks do not yield basic metals such as copper, tin and iron, which were so important to the developing cultures of Asia and Europe. Polynesian implements were made of varieties of volcanic rock, limestone (reefrock and beachrock), various woods and plants, bones (including those of humans), shells and the like. Pottery was not produced owing in part to the poor clays generated from the weathering of volcanic rock. Mortar and other types of cement were not used since the Polynesians did not possess that technology, even though limestone is rather plentiful around many of the islands. Obviously this is a good example of how the physical setting affects human cultural development, especially as seen through the eyes of an archaeologist/anthropologist.
Finally, it is interesting to note the changes in the interpretation of the geologic history of the Hawaiian Islands over the last few decades. It might surprise you to know that it was not until the early 1960's, that the geological theories of plate tectonics and magmatic hot spots originated and that the first radiometric dates of the island's volcanic rocks were published. Before that most geologists thought that the Hawaiian Islands had been produced by volcanic eruptions along a long fissure in the oceanic crust. Relative ages of the high volcanic islands, generally with Kauai being the oldest and Hawaii being the youngest, were based on degrees of erosion and the biogeographic distribution of native plants and animals. It is only somewhat recent thought which indicates that Hawaii's volcanic mountain/islands were formed successively as the 3-5 mile thick oceanic crust of the Pacific Tectonic Plate moved northwestward (at a rate of about 3.4 inch/yr) across the Hawaiian Magmatic Hot Spot.
So what can be expected for Kauai? Nihoa is the next Hawaiian island to the northwest. It is an uninhabitable rock less than a mile long and less than 900 ft high, compared with the Garden Island of Kauai which is 33 miles long and over 5,200 ft high. Nihoa's volcanic rocks have been dated at 7.2 million years, compared with Kauai at 5.1 million years. Assuming that Nihoa was at least 5,000 ft high 2.1 million years ago, Kauai would have to subside and be eroded at a rate of 2,050 ft/million years (or at about 1 inch every 40 years) to reach that level. Nihoa is 162 miles northwest of Kauai. With the Pacific Tectonic Plate moving at 3.4 inch/yr it would take about 3,035,000 years for Kauai to move to Nihoa's present location. Using such scenarios, one can estimate that it will take something around 2 to 3 million years for Kauai to be transformed from one of the Earth's most beautiful islands to one preferred mainly by sea birds.