Cosmogenic dating basalt
A recently published K→Ar age of 26±5ka was sampled within a few hundred meters of three of our cosmogenic exposure age samples and appears to be from the same basalt flow.Given the large uncertainties associated with dating young lava flows, the K→Ar age and our cosmogenic ages are in reasonable agreement; however, they do not overlap within uncertainties and suggest possible systematic discrepancies between the two methods of up to 20% in this instance.This volcanic hiatus is similar in duration to that observed in the Canary Islands. The northwestern part of the field, called Los Volcanes, includes multiple basaltic lava flows and numerous cinder cones and scoria fields.Assuming a constant rate of production, the number of atoms of Be-10 and Al-26 that accumulate in a rock surface will be proportional to the length of time the rocks were exposed to cosmic ray bombardment and the respective rates of radioactive decay for each isotope.An age determined by measurement of the amount of each nuclide would be an estimate of the age of the surface exposure, that is, the surface could have been exposed for much longer than the minimum calculated age.Cosmogenic isotopes are created when elements in the atmosphere or earth are bombarded by high energy particles (-mesons and protons, collectively known as cosmic rays) that penetrate into the atmosphere from outer space.Some cosmic ray particles reach the surface of the earth and contribute to the natural background radiation environment.
Jiří Hála's textbook states that soils vary greatly in their ability to bind radioisotopes, the clay particles and humic acids can alter the distribution of the isotopes between the soil water and the soil.
The post-collapse flows have exposure ages ranging from 62 to 11 ka.