The analytical equipment used to determine the abundances of isotopes is more accurate in determining ratios of isotopes than their absolute abundances.
Potassium-40 (Rb has occurred since the rock cooled from the lava flow.
Do analyses of the radioactive isotopes of rocks give reliable estimates of their ages?
That is a good question, which ordinarily requires a lengthy and technical answer.
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. Cannon-like, highly explosive eruptions in January and March 1974 threw out large quantities of ash as a column into the atmosphere, and as avalanches flowing down the cone’s sides.