Geologists know the exact chemical composition of this tephra ( which they call Mazama Ash ) and both geologists and archeologists use the distinctive layer it formed in the specific techniques of relative dating called tephrochronology.
12.
Radiocarbon dating and tephrochronology has evidenced Holocene activity at Burney . 2, 320 ?100 and 7, 450 ?500 BCE large Plinian eruptions with a volcanic explosivity index of 5 generated the MB2 and MB1 tephras, respectively.
13.
Radiocarbon dating and tephrochronology indicate five other eruptions predating the historical records in the approximate years 1350, 550 BC, 1050 BC, 3900 BC ?00 years, 7050 BC . The eruption in 7050 BC was the largest with a VEI of 3.
14.
Researchers have studied other radioactive isotopes created by cosmic rays to determine if they could also be used to assist in dating objects of archaeological interest; such isotopes include thermoluminescence, optically stimulated luminescence, electron spin resonance, and fission track dating, as well as techniques that depend on annual bands or layers, such as dendrochronology, tephrochronology, and varve chronology.
15.
Tephrochronology and radiocarbon dating indicate that Glacier Peak eruptions occurred in 1700 AD ?100 years, 1300 AD ?300 years, 900 AD ?50 years, 200 AD ?50 years, 850 BC, 3150 BC, and in 3550 BC . The Volcanic Explosivity Index ( VEI ) for three of these was 2 to 4, small compared to the 5 of the 1980 eruption of Mount St . Helens.
