Radio-dating in Rubble
by Keith Swenson
In August of 1993, with geologist Dr Steven Austin and others from the Institute for Creation Research, I climbed into the crater of Mount St Helens to view the lava dome. It was one of those experiences that was well worth every exhausting moment! The dome (Geology of the Grand Canyon figure, shown in More and more wrong dates) looks like a small mountain, roughly 1.1 km (¾ mile) long and 350 m (1,100 ft) high. 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 18 May 1980.1 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.
Actually, the present lava dome at Mount St Helens is the third dome to form since the 1980 eruption, the previous two having been blasted away by the subsequent eruptions.
The current dome started growing after the volcano’s last explosive eruption on 17 October 1980. During 17 so-called dome-building eruptions, from 18 October 1980 to 26 October 1986, thick pasty lava oozed out of the volcanic vent like toothpaste from a tube.1
Dacite lava is too thick to flow very far, so it simply piled up around the vent, forming the mountain-like dome, which now plugs the volcanic orifice.
How radioactive ‘dating’ really works
Why does the lava dome provide an opportunity to test the accuracy of radioisotope dating? There are two reasons. First, radioisotope-dating methods are used on igneous rocks—those formed from molten rock material. Dacite fits this bill. Fossil-bearing sedimentary rock cannot be directly dated radioisotopically. Second, and most importantly, we know exactly when the lava dome formed. This is one of the rare instances in which, to the question, ‘Were you there?’ we can answer, ’Yes, we were!’
The dating method Dr Austin used at Mount St Helens was the potassium-argon method, which is widely used in geological circles. It is based on the fact that potassium-40 (an isotope or ‘variety’ of the element potassium) spontaneously ‘decays’ into argon-40 (an isotope of the element argon).2 This process proceeds very slowly at a known rate, having a half-life for potassium-40 of 1.3 billion years.1 In other words, 1.0 g of potassium-40 would, in 1.3 billion years, theoretically decay to the point that only 0.5 g was left.
Contrary to what is generally believed, it is not just a matter of measuring the amount of potassium-40 and argon-40 in a volcanic rock sample of unknown age, and calculating a date. Unfortunately, before that can be done, we need to know the history of the rock. For example, we need to know how much ‘daughter’ was present in the rock when it formed. In most situations we don’t know since we didn’t measure it, so we need to make an assumption—a guess. It is routinely assumed that there was no argon initially. We also need to know whether potassium-40 or argon-40 have leaked into, or out of, the rock since it formed. Again, we do not know, so we need to make an assumption. It is routinely assumed that no leakage occurred. It is only after we have made these assumptions that we can calculate an ‘age’ for the rock. And when this is done, the ‘age’ of most rocks calculated in this way is usually very great, often millions of years. The Mount St Helens lava dome gives us the opportunity to check these assumptions, because we know it formed just a handful of years ago, between 1980 and 1986.
The dating test
In June of 1992, Dr Austin collected a 7-kg (15-lb) block of dacite from high on the lava dome. A portion of this sample was crushed and milled into a fine powder. Another piece was crushed and the various mineral crystals were carefully separated out.3 The ‘whole rock’ rock powder and four mineral concentrates were submitted for potassium-argon analysis to Geochron Laboratories of Cambridge, MA—a high-quality, professional radioisotope-dating laboratory. The only information provided to the laboratory was that the samples came from dacite and that ‘low argon’ should be expected. The laboratory was not told that the specimen came from the lava dome at Mount St Helens and was only 10 years old.
The results of this analysis are shown in Table 1. What do we see? First and foremost that they are wrong. A correct answer would have been ‘zero argon’ indicating that the sample was too young to date by this method. Instead, the results ranged from 340,000 to 2.8 million years! Why? Obviously, the assumptions were wrong, and this invalidates the ‘dating’ method. Probably some argon-40 was incorporated into the rock initially, giving the appearance of great age. Note also that the results from the different samples of the same rock disagree with each other.
by Keith Swenson
In August of 1993, with geologist Dr Steven Austin and others from the Institute for Creation Research, I climbed into the crater of Mount St Helens to view the lava dome. It was one of those experiences that was well worth every exhausting moment! The dome (Geology of the Grand Canyon figure, shown in More and more wrong dates) looks like a small mountain, roughly 1.1 km (¾ mile) long and 350 m (1,100 ft) high. 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 18 May 1980.1 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.
Actually, the present lava dome at Mount St Helens is the third dome to form since the 1980 eruption, the previous two having been blasted away by the subsequent eruptions.
The current dome started growing after the volcano’s last explosive eruption on 17 October 1980. During 17 so-called dome-building eruptions, from 18 October 1980 to 26 October 1986, thick pasty lava oozed out of the volcanic vent like toothpaste from a tube.1
Dacite lava is too thick to flow very far, so it simply piled up around the vent, forming the mountain-like dome, which now plugs the volcanic orifice.
How radioactive ‘dating’ really works
Why does the lava dome provide an opportunity to test the accuracy of radioisotope dating? There are two reasons. First, radioisotope-dating methods are used on igneous rocks—those formed from molten rock material. Dacite fits this bill. Fossil-bearing sedimentary rock cannot be directly dated radioisotopically. Second, and most importantly, we know exactly when the lava dome formed. This is one of the rare instances in which, to the question, ‘Were you there?’ we can answer, ’Yes, we were!’
The dating method Dr Austin used at Mount St Helens was the potassium-argon method, which is widely used in geological circles. It is based on the fact that potassium-40 (an isotope or ‘variety’ of the element potassium) spontaneously ‘decays’ into argon-40 (an isotope of the element argon).2 This process proceeds very slowly at a known rate, having a half-life for potassium-40 of 1.3 billion years.1 In other words, 1.0 g of potassium-40 would, in 1.3 billion years, theoretically decay to the point that only 0.5 g was left.
Contrary to what is generally believed, it is not just a matter of measuring the amount of potassium-40 and argon-40 in a volcanic rock sample of unknown age, and calculating a date. Unfortunately, before that can be done, we need to know the history of the rock. For example, we need to know how much ‘daughter’ was present in the rock when it formed. In most situations we don’t know since we didn’t measure it, so we need to make an assumption—a guess. It is routinely assumed that there was no argon initially. We also need to know whether potassium-40 or argon-40 have leaked into, or out of, the rock since it formed. Again, we do not know, so we need to make an assumption. It is routinely assumed that no leakage occurred. It is only after we have made these assumptions that we can calculate an ‘age’ for the rock. And when this is done, the ‘age’ of most rocks calculated in this way is usually very great, often millions of years. The Mount St Helens lava dome gives us the opportunity to check these assumptions, because we know it formed just a handful of years ago, between 1980 and 1986.
The dating test
In June of 1992, Dr Austin collected a 7-kg (15-lb) block of dacite from high on the lava dome. A portion of this sample was crushed and milled into a fine powder. Another piece was crushed and the various mineral crystals were carefully separated out.3 The ‘whole rock’ rock powder and four mineral concentrates were submitted for potassium-argon analysis to Geochron Laboratories of Cambridge, MA—a high-quality, professional radioisotope-dating laboratory. The only information provided to the laboratory was that the samples came from dacite and that ‘low argon’ should be expected. The laboratory was not told that the specimen came from the lava dome at Mount St Helens and was only 10 years old.
The results of this analysis are shown in Table 1. What do we see? First and foremost that they are wrong. A correct answer would have been ‘zero argon’ indicating that the sample was too young to date by this method. Instead, the results ranged from 340,000 to 2.8 million years! Why? Obviously, the assumptions were wrong, and this invalidates the ‘dating’ method. Probably some argon-40 was incorporated into the rock initially, giving the appearance of great age. Note also that the results from the different samples of the same rock disagree with each other.
