This is the broad definition of tephra (Greek tephra, "ash") proposed by the Icelandic volcanologist Sigurður Þórarinsson (Sigurdur Thorarinsson) in 1954, in connection with the eruption of Hekla (Thorarinsson, "The eruption of Hekla, 1947-48II, 3, The tephra-fall from Hekla, March 29th, 1947", Visindafélag Íslendinga (1954:1-3). The term had been used earlier in Sigurdur Thorarinsson's 1944 doctoral studies, but not in English. See Thorarinsson, S (1944). "Tefrokronologiska studier pA Island". Geografiska Annaler. 26 (1–2): 1–217. doi:10.1080/20014422.1944.11880727.