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The potassium-argon (K–Ar) dating method is often used to date volcanic rocks (and by extension, nearby fossils). Eleven samples were collected from five recent lava flows during field work in January 1996—two each from the 11 February 1949, 4 June 1954, and 14 July 1954 flows and from the 19 February 1975 avalanche deposits, and three from the 30 June 1954 flow14 (Figure 6).
In using this method, it is assumed that there was no daughter radiogenic argon (Ar*) in rocks when they formed.13 For volcanic rocks which cool from molten lavas, this would seem to be a reasonable assumption. Inset: Andesite of the June 30, 1954 flow, Mt Ngauruhoe, seen at 60 times magnification under a geological microscope. The darker recent lavas were clearly visible and each one easily identified (with the aid of maps) on the northwestern slopes against the lighter-coloured older portions of the cone (Figures 4 and 7).
Eruptions from a central 400 m (1,300 foot) wide crater have constructed the cone’s steep (33°) outer slopes.In last Tuesday’s lecture, radiocarbon dating was covered briefly.It is an essential technology that is heavily involved in archaeology and should be explored in greater depth.The 18 August flow was more than 18 m (55 feet) thick and still warm almost a year after congealing.Explosions of ash completed this long eruptive period.