It is composed of a volcanic rock called dacite and appears to an observer in the crater as a huge steaming mound of dark, blocky rubble. Helens is the third dome to form since the 1980 eruption, the first two having been blasted away by subsequent eruptions.
Why does the lava dome provide an opportunity to test the accuracy of radioisotope dating? First, radioisotope dating methods can be used mainly on volcanic (igneous) rock, such as dacite.
(Fossil-bearing sedimentary rock cannot be directly dated radioisotopically.) Second, the date of formation of the dacite is known.
If the methods don’t work on rocks of known age, it is most unreasonable to trust that they work on rocks of unknown age.
It is far more rational to trust the Word of the God who created the world, knows its history perfectly, and has revealed sufficient information in the Bible for us to understand that history and the age of the creation.
Geologists agree that these volcanoes erupted only thousands of years ago, spilling lava into an already eroded Grand Canyon, even temporarily damming the Colorado River.