An interesting and informative study that explains how ice cores have a volcanic signature and how it is possible to pinpoint specific eruptions – go to https://archaeologynewsnetwork.blogspot.com/2019/08/synchronization-of-i… … during a volcanic eruption, gases, lava, rocks and tiny ash particles are ejected into the atmosphere. The smallest particles are carried by the wind and transported for miles until they drop out on to the surface of the earth – including over the ice sheet on Greenland. Ash that landed on that particular ice sheet thousands of years ago can be retrieved by drilling long ice cores etc.
Many of the ash particles are so small they are not visible to the naked eye. Only when a large amount of ash particles is present in a layer will the layer be visible – but most ash layers are invisible. Yet scientists search out these ash layers in ice cores that can be 3km in length. They are valuable to scientists as the layers can be used as reference horizons (pinpointing where one is in one core as opposed to another core). They are catalogued into an archive. Each ash layer has a chemical signature and these can be used to assign the ash to various volcanoes – and which eruption of that volcano. The high acidity of the ash, as a result of volcanic sulphur, leads to high electrical conductivity in the ice. It is fast and easy to measure the electrical conductivity of the ice, and the acid peaks, which is a useful clue and is a guide for where the tiny ash particles might be hiding. See also Science Advances at https://doi.org/10.1126/sciadv.aaw4621