<P> The last to form, and the highest cone, the Hotlum Cone, formed about 8,000 years ago . It is named after the Hotlum glacier on its northern face; its longest lava flow, the 500 - foot - thick (150 - metre) Military Pass flow, extends 5.5 mi (8.9 km) down its northeast face . Since the creation of the Hotlum Cone, a dacite dome intruded the cone and now forms the summit . The rock at the 600 - foot - wide (180 - metre) summit crater has been extensively hydrothermally altered by sulfurous hot springs and fumaroles there (only a few examples still remain). </P> <P> In the last 8,000 years, the Hotlum Cone has erupted at least eight or nine times . About 200 years ago the last significant Mount Shasta eruption came from this cone and created a pyroclastic flow, a hot lahar (mudflow), and three cold lahars, which streamed 7.5 mi (12.1 km) down Mount Shasta's east flank via Ash Creek . A separate hot lahar went 12 mi (19 km) down Mud Creek . This eruption was thought to have been observed by the explorer La Pérouse, from his ship off the California coast, in 1786, but this has been disputed . </P> <P> During the last 10,000 years, Mount Shasta has erupted an average of every 800 years, but in the past 4,500 years the volcano has erupted an average of every 600 years . The last significant eruption on Mount Shasta may have occurred about two centuries ago . </P> <P> Mount Shasta can release volcanic ash, pyroclastic flows or dacite and andesite lava . Its deposits can be detected under nearby small towns . Mount Shasta has an explosive, eruptive history . There are fumaroles on the mountain, which show Mount Shasta is still alive . </P>

When was the last time mount shasta was active