A 29% reduction in area of the Brown Glacier from 1947-2003 was observed. The volcano Big Ben, from which all the glaciers drain, has shown no sign of changing geothermal output to cause the melting; a 1 degree Celsius warming has occurred over the same time period. Glaciologists continue to study the Brown Glacier, detailing surveys of the glacier's snout and surface, which determine if glacial retreat is rapid or punctuated.