Recent Significant Eruptive Activity

Summary

According to the Global Volcanism Program, run by the Smithsonian Institution, significant eruptions occurred most recently in 2005, particularly from March to June.  It appears that this year marked a substantial increase in the intensity of Colima's activity, as the number of days in which ash plumes rose about 2km over the summit increased from 3 days in 2000 to 31 days in only the first half of 2005.  Large, notable eruptions began in March 2005, producing pyroclastic flows and eruption plumes of ash that continued into July.  At the peak of the eruptive activity, from around April to June, pyroclastic flows reached distances of about 5.1km, and columns of ash rose about 10km above Colima's summit.  These eruptions destroyed the lava dome that had formed in the eruptions of September-November 2004, replacing it with dome and unconsolidated material for a period until larger eruptions left it an empty crater that measured about 260m across and 30m deep⁴. 

Before                                                                                                 After

Fig. 1 Colima on May 25 2005 before the accumulated material was expelled by a large eruption.

Fig. 2 Colima on June 16 2005 following the large eruption that cleared the dome.

VEI (Volcanic Explosivity Index)

3

A VEI of 3 indicates a rather severe eruption of a frequency that normally does not exceed yearly occurrence.  This classification is assigned to eruptions emitting ash plumes ranging in height from 3-15 km and is appropriate due to the emission of at least one ash column of about 10 km in altitude. That part of an existing lava dome was destroyed, as well as the presence of extensive pyroclastic flows, are also testament to its severity.  However, a VEI of 2 could be assigned to a substantial amount of the activity, due to its explosive, yet less intense nature in terms of mass of ejecta, plume height, and pyroclastic flow length. 

Mercalli Classification

Vulcanian

This eruption was classified by the Smithsonian Institution as Vulcanian.  This classification was assigned due to:

1. The explosivity, rather than effusiveness, of the eruption, which rules out Hawaiian and most Strombolian eruptions

2. The violent ejection of tephra, including old material and new ash, several kilometers into the atmosphere, dispersing it over a vast area but not the extent of a Plinian eruption.

3. The presence of pyroclastic flows.