Crystals found in the ancient derrubes of volcanoes can be used to predict eruptions. This is what they have come to the conclusion that the volcano Mount St. Helens investigated the ash emitted before its explosive eruption in 1980.
To investigate the possibility of a volcano suffering a severe eruption, geologists investigate the material emitted by the volcano in search of the remains that the magma is approaching. Previously, vitreous material was sought, since they believed that the magma cools too quickly to produce crystals. TPV. In Helens no vitreous materials were found, so the eruption had not been planned.
Since then it has been known that if the magma has water crystals can form. With this, they have rechecked the ashes and have found small crystals. These crystals indicate that the magma was making the upward path causing an explosive eruption. This discovery can serve to predict future eruptions.