It is not as well publicized as its larger close neighbour Mt Ruapehu, which has erupted briefly several times in the last five years. However, Mt Ngauruhoe is an imposing, almost perfect cone that rises more than 1, metres 3, feet above the surrounding landscape to an elevation of 2, m 7, feet above sea level 1 Figure 3. Mt Ngauruhoe is thought to have been active for at least 2, years, with more than 70 eruptive periods since , when European settlers first recorded a steam eruption. The first lava eruption seen by Europeans occurred in The eruption lasting from 13 May to 10 March began with an explosive ejection of ash and blocks.
Sample Preparation and Amounts | OSU Argon Geochronology Laboratory
The older method required splitting samples into two for separate potassium and argon measurements, while the newer method requires only one rock fragment or mineral grain and uses a single measurement of argon isotopes. The sample is generally crushed and single crystals of a mineral or fragments of rock hand-selected for analysis. These are then irradiated to produce 39 Ar from 39 K. The sample is then degassed in a high-vacuum mass spectrometer via a laser or resistance furnace. Heating causes the crystal structure of the mineral or minerals to degrade, and, as the sample melts, trapped gases are released. The gas may include atmospheric gases, such as carbon dioxide, water, nitrogen, and argon, and radiogenic gases, like argon and helium, generated from regular radioactive decay over geologic time. The J factor relates to the fluence of the neutron bombardment during the irradiation process; a denser flow of neutron particles will convert more atoms of 39 K to 39 Ar than a less dense one.
Potassium-Argon Dating Methods
Potassium-argon dating , method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock. This dating method is based upon the decay of radioactive potassium to radioactive argon in minerals and rocks; potassium also decays to calcium Thus, the ratio of argon and potassium and radiogenic calcium to potassium in a mineral or rock is a measure of the age of the sample. The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium.
O Timothy, keep that which is committed to thy trust, avoiding profane and vain babblings, and oppositions of science falsely so called: Which some professing have erred concerning the faith. Lies of Evolution: K-Ar Dating. Author: Christopher J. Johnson Published: Dec 20, Updated: Apr 8,