The Rarotonga hotspot is a volcanic hotspot in the southern Pacific Ocean. The hotspot was responsible for the formation of Rarotonga and some volcanics of Aitutaki. In addition to these volcanoes in the Cook Islands, the composition of volcanic rocks in Samoa and in the Lau Basin may have been influenced by the Rarotonga hotspot, and some atolls and seamounts in the Marshall Islands may have formed on the hotspot as well. Geology Oceanic plateaus and linear volcanic chains dot the floor of the Pacific Ocean. Their formation has been explained with mantle plumes which rise from the core-mantle boundary and spread out when they rise, forming a large "head" that causes intense volcanic activity once it hits the crust. This volcanism is responsible for the formation of the oceanic plateaus. Later, the remnant "tail" of the plume is still rising and induces the formation of volcano chains as the crust moves over the plume tail, thus forming the linear chains. A number of hotspots are or were active in the Pacific Ocean and some of these may be the product of mantle plumes. Other hotspots such as Rarotonga appear to have been active only for short time periods; many of these are located in French Polynesia where there is a superswell. Such hotspot volcanism may be the product of shallow processes. Later research has suggested however that the Macdonald hotspot, the Rarotonga hotspot and the Rurutu hotspot are long lived hotspots that were active as far back as the Cretaceous; they may be over 100 million years old and in such case the oldest still active hotspots in the Pacific. These hotspots together may have built the Cook-Austral Islands together, resulting in overlapping ages of the volcanoes. Seismic tomography has found slow velocity anomalies underneath the Rarotonga hotspot, down to depths of about with more recent research indicating that they root at about depth. The anomaly lies at over depth with no evidence of shallower anomalies, however. The Rarotonga hotspot and other regional hotspots appear to be anchored to a deep mantle structure called a large low shear-wave velocity province. Products The Rarotonga hotspot is reliably linked only to the formation of Rarotonga and to volcanism on Aitutaki, potential volcanic structures between the Tonga Trench and Rarotonga that may have been formed by the same hotspot are poorly studied. Rarotonga itself is young but there is little indication of