Rising mantle temperatures and two heat surges may explain why some Hawaiian volcanoes grew exceptionally large. A 3500 km (2200 mile) trail of volcanoes records the Pacific plate’s slow passage over the Hawaiian hotspot. Instead of cooling through time as geologists have generally expected, the mantle plume beneath this chain appears to have warmed by about 250°C (480°F) during the past 47 million years. Together, the two datasets allowed the researchers to trace how plume temperature and lava production changed across millions of years along the Hawaiian Ridge. Two heat surges built the giantsThe results point to an overall rise in lava temperature interrupted by two major surges of heat.