Rapilli (/rɑːˈpɪli/) is a volcanic term referring to small fragments of lava less than 2 mm in diameter. The word is derived from the Latin word "rapilli," meaning "little stones" or "gravel." The IPA phonetic transcription of this word represents the sounds of the initial "r" sound, the long "a" vowel sound, and the voiceless "p" and "l" sounds. The double "l" indicates a single consonant sound, while the final "i" represents the plural form of the word.
Rapilli is a geological term used to describe a type of volcanic rock fragment that is smaller than lapilli but larger than volcanic ash. It is typically between 2 and 64 millimeters in diameter and is formed during explosive volcanic eruptions.
Rapilli are made up of pyroclastic material, which refers to fragments that are ejected during volcanic eruptions. These fragments can be composed of various materials, such as lava, liquid rock, and gas. Rapilli are characterized by their porous and vesicular nature, which is a result of trapped gas bubbles within the fragment.
The formation of rapilli occurs when the magma within a volcano is rapidly cooled and solidifies into small fragments due to the violent and explosive nature of certain volcanic eruptions. As the fragmented magma is ejected into the atmosphere, it undergoes rapid cooling, causing the lava to solidify into small, irregularly shaped pieces. These pieces are then deposited around the volcanic vent or spread over the surrounding landscape as part of the pyroclastic flow.
Rapilli play a significant role in deciphering the eruptive history of a volcano. Geologists can analyze the composition and size distribution of rapilli to determine the type of volcanic eruption that produced them. Additionally, studying rapilli can also provide insights into the dynamics of volcanic eruptions and the conditions within the volcano during its formation.
The word "rapilli" is derived from the Latin word "rapilli", which is the plural form of "rapillus". "Rapillus" itself is a diminutive of the Latin word "rapa", meaning "turnip". In Ancient Rome, "rapilli" referred to fragments of volcanic material typically smaller than lapilli (pebble-sized volcanic fragments). These fragments were often associated with pyroclastic flows from volcanic eruptions and were formed when hot, solidified lava exploded into the air and shattered into small pieces during a volcanic eruption. Today, the term "rapilli" is commonly used within the field of volcanology to describe volcanic rock fragments of this size.