Lapilli, meaning ‘littlestones’ in Latin, can have diverse origins, but the example show

Lapilli, meaning ‘littlestones’ in Latin, can have diverse origins, but the example shown on aphotograph is more precisely called accretionary lapilli.Accretionarylapilli form during a volcanic eruption in the ash cloud. When big volcaniceruption occurs, a volcano will blow a huge cloud into the atmosphere. Such cloudwill contain massive boulders, smaller rocks, volcanic ash and gases etc.Rocks are heavy, so they fall back down fast, however, ash and gases do not. Themost abundant and important in this process gas is a water vapour. Mix fine ash and watervapour/steam together and what you get is an airborne mud. Water vapour sticks ashparticles together, so as the huge turbulent ash cloud grows and mixes, moreand more ash particles come together to form little balls (lapilli) whichthen rain down like hail once they get too heavy.This layer formedafter such rock rain in Hawai’i Island (Big Island). -- source link
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