New Delhi:
Researchers have found out the cause behind largest volcanic eruptions that occurred 73,000 years ago. At that time, huge volumes of volcanic ash were ejected into the atmosphere and also rained that covered enormous areas in India and Indonesia.
Geochemical clues inside volcanic quartz crystals were helpful while finding the secret behind the volcanic eruptions.
The deadly volcanoes on earth are called supervolcanoes. These are capable of producing cataclysmic eruptions that destroy huge regions and also create global cooling in the overall climate.
Toba, the Indonesian supervolcano, had one of these eruptions approximately 73,000 years ago and at that time, 2,800 cubic kilometres of volcanic ash was thrown into the atmosphere and rained down covering many areas in Indonesia and India.
Scientists have always discussed as to how this much volume of magma is generated and what makes this magma erupt in the explosive way.
Well, a team of researchers at Uppsala University in Sweden, together with international colleagues, have found out fascinating clues that are hidden inside millimetre-sized crystals in volcanic ash and rock.
“Quartz crystals that grow in the magma register chemical and thermodynamical changes in the magmatic system prior to eruption, similar to how tree rings record climate variations,” said David Budd from Uppsala University.
“When the conditions in the magma change, the crystals respond and produce distinct growth zones that record these changes. The problem is that each “tree ring”-analogue is only a few micrometres across, which is why they are extremely challenging to analyse in detail,” said Budd.
Quartz crystals from Toba were observed by the researchers. They found a distinct change in the isotopic composition towards the outer rim of the crystals. The crystal rims contain a relatively lower proportion of the heavy isotope 18O compared to the lighter 16O.
“The low ratio of 18O to 16O contents in the crystal rims indicate that something in the magmatic system changed drastically just before the big eruption,” said Frances Deegan from Uppsala University.
The explanation behind these chemical signatures is that the magma melted and integrated to form a rock that is charcterised by a relatively low ratio of 180 to 160.
This rock type also often contains a lot of water, which may be released into the magma, producing steam, and thereby an increased gas pressure inside the magma chamber.
“This rapidly increased gas pressure eventually allowed the magma to rupture the overlying crust, and send thousands of cubic kilometres of magma into the atmosphere,” Deegan added.
