tephra SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O total Ref Hekla 4 Tephra 74.31 0.13 12.84 1.83 0.09 0.07 1.34 4.66 2.73 98.05 854 Hekla 4 Tephra 72.95 0.11 12.91 1.88 0.08 0.13 1.31 4.93 2.83 97.03 854 Hekla 4 Tephra 72.69 0.10 12.79 1.77 0.10 0.01 1.24 4.62 2.81 96.16 854 Hekla 4 Tephra 72.39 0.04 12.72 1.79 0.14 0.00 1.23 4.78 2.84 95.97 854 Hekla 4 Tephra 72.26 0.09 12.64 1.92 0.05 0.01 1.34 4.69 2.69 95.73 854 Hekla 4 Tephra 72.12 0.11 12.63 1.83 0.11 0.04 1.14 4.56 2.70 95.29 854 Hekla 4 Tephra 71.99 0.06 12.46 1.89 0.13 0.01 1.29 4.55 2.70 95.07 854 Hekla 4 Tephra 71.77 0.12 12.62 1.96 0.06 0.01 1.21 4.94 2.68 95.40 854 Hekla 4 Tephra 71.40 0.14 12.53 1.79 0.13 0.03 1.39 4.72 2.97 95.11 854 ------------------------------------------------------------------------ 854: Pilcher, J.R., Hall, V.A., and McCormac, F.G. (1995) Dates of Holocene Icelandic volcanic eruptions from tephra layers in Irish peats.. The Holocene 5(1), 103-110.