Mt Ngauruhoe is thought to have been active for at least 2,500 years, with more than 70 eruptive periods since 1839, when European settlers first recorded a steam eruption.
The current dome started growing after the volcano’s last explosive eruption on 17 October 1980.This lava was not hot enough to melt olivine, so the chunks were carried along when the eruption brought lava up from the depths.Of course the olivine inclusions dated as being old. In fact, the scientists weren't trying to date the olivine inclusions - the xenoliths.Notice the title of the actual scientific report: The important word here is "Inclusions".The scientists were not out to date the lava: they were dating some chunks of olivine that were stuck in the lava like raisins.Various creationist books mention the 1801 eruption of the Hualalai volcano in Hawaii.
They claim that scientists dated the 200 year old lava, and got the utterly bogus age of 22 million years.
It sits directly over the volcanic vent at the south end of the huge horseshoe-shaped crater that was blasted out of the mountain by the spectacular eruption on .1 From the crater, the dome appears as a huge steaming mound of dark, block-like rubble.
It is made of dacite, a fine-grained volcanic rock that contains a sprinkling of larger, visible crystals, like chopped fruit in a cake.
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.
Popular Dating Methods Both the K-Ar and Rb-Sr methods make use of radioactive decay of a parent isotope to a stable daughter isotope. Leeman, "Late Cenozoic Alkali-Rich Basalt from the Western Grand Canyon Area, Utah and Arizona: Isotopic Composition of Strontium," Geological Society of America Bulletin, 85 (Nov. Six analyses of Uinkaret Plateau basalts (U-33, U-35, U-59, U-24, U-43, U-58) were used.