A major volcanic event in 1257 – 1258 was first discovered from data in ice cores ; specifically increased sulfate concentrations were found in 1980 within the Crête ice core ( Greenland , drilled in 1974 ) associated with a deposit of rhyolitic ash . The 1257-1258 layer is the third largest sulfate signal at Crête ; at first a source in a volcano near Greenland had been considered but Icelandic records made no mention of eruptions around 1250 and it was found in 1988 that ice cores in Antarctica – at Byrd Station and the South Pole – also contained sulfate signals . Sulfate spikes were also found in ice cores from Ellesmere Island , Canada , and the Samalas sulfate spikes were used as stratigraphic markers for ice cores even before the volcano that caused them was known . The ice cores indicated a large sulfate spike , accompanied by tephra deposition , around 1257 - 1259 , the largest in 7,000 years and twice the size of the spike due to the 1815 eruption of Tambora . In 2003 , a dense rock equivalent volume of was estimated for this eruption , but it was also proposed that the eruption might have been somewhat smaller and richer in sulfur . The volcano responsible was thought to be located in the Ring of Fire but could not be identified at first ; Tofua volcano in Tonga was proposed at first but dismissed , as the Tofua eruption was too small to generate the 1257 sulfate spikes . A volcanic eruption in 1256 at Harrat al-Rahat near Medina was also too small to trigger these events . Other proposals included several simultaneous eruptions . Estimated diameters and positions of the calderas left by the eruption ranged from , close to the equator and probably north of it
1815 eruption of Tambora
1815 eruption of Mount Tambora
1257 Samalas eruption