To date, Van Tilburg and the Easter Island Statue Project (EISP) have inventoried 887 monolithic statues (moai) and compiled a metric database buttressed by 24,000 original and archived images. Some 35% of the known statues are located on or in direct relation to ceremonial sites called image ahu (Martinsson – Wallin 1994: Appendix 1 gives 164 image ahu; Van Tilburg 1986; Van Tilburg and Vargas C. 1998).
Rano Raraku, a volcanic crater on the island’s eastern plain, was the source of the sideromelane (basaltic) tuff from which 95% of the statues were carved. This source is irrefutable as there are 397 in situ statues, of which 141 in various stages of completion have recently been mapped by EISP in the interior quarries (Van Tilburg 2005; www.eisp.org). Much rarer statue lithologies are basalt (hawaiite lavas) from three named regions; trachyte and ‘red basaltic scoria’ or ‘red scoriaceous lava’ (also used as pukao or ‘topknots’ that were placed on the heads of about 75-100 statues).
There are only 20 statues (portable and non-portable) now in the EISP database which were carved of basalt. Of these, 7 are in museum collections. The British Museum holds two basalt statues, both of which are of central and very great significance to furthering our understanding of Rapa Nui history. One of them (1869.10-5.1) is re-carved on its dorsal side with bas-relief and incised petroglyphs of great iconographic significance. This re-carving is unique in its style, detail, and expertise and quality of execution. Four other statues, including 1869.10-6.1 (Moai Hava), have incised petroglyphs of lesser distinction but within clearly defined, limited typological categories. Another 30 statues still in situ on the island have applied decorations of similar styles.