Cotopaxi THE DANGER WITHIN

DAN GLEASON

ERUPTIVE HISTORY

The eruptive history of Cotopaxi extends back to about the year 2640 B.C. Evidence from this first historic eruption has been found in ancient pyroclastic flow, debris flow and lahar deposits, which suggest a large explosive eruption, which likely resulted in fatalities to any creatures living relatively near the vent.² There is evidence of various explosive eruptions over the following 4,500 years, with quiescent periods ranging from 1,400 years to 40 years.² Although the VEI of these eruptions is unknown, evidence of pyroclastic flows, lava flows, and lahars has been found for some of them.²

The oldest confirmed eruption with a known VEI is the eruption of June, 1534, which had a VEI of 4 and devastated the surrounding land with ash fall, pyroclastic flows and lahars.² Following this, there was little to no recorded activity for over a century, followed by a frenzy of activity from the late 1600's to the late 1800's, with eruptions ranging in VEI of 2 to 4, and happening as frequently as twice a year.² The destructiveness of these eruptions culminated in the eruption of 1877 (VEI 4), during which the snow and ice of the summit and flank of Cotopaxi was melted, causing a lahar that famously travelled over 300 km and reached the Pacific Ocean as well as the Amazon basin.^2*

Cotopaxi has calmed down significantly in the last century, having had no confirmed eruptions since 1940, and no eruptions with a VEI of more than 2 since 1903.² No pyroclastic flows or significant lahars have occurred since the 1903 eruption, which had a VEI of 3 and didn't end until December of 1904.² However, in 2001 the seismic activity of Cotopaxi increased drastically, spiking in 2002. It has decreased since then, and volcanologists attributed much the activity to a movement of gas rather than a new injection of magma.²

A measure of registered monthly seismic activity from 1989 to 2002.²

  Date       Long-period        Hybrid             Volcano-tectonic
               Total Daily avg.   Total Daily avg.   Total Daily avg.

    Jan 2001    336    10.8          0     0.0         18     0.6
    Feb         185     6.6          0     0.0          4     0.1
    Mar         319    10.3          1     0.0         10     0.3
    Apr         280     9.3          0     0.0         26     0.9
    May         241     7.8          7     0.2         10     0.3
    Jun         243     8.1         11     0.4         53     1.8
    Jul         262     8.5          2     0.1          9     0.3
    Aug         241     7.8          0     0.0          9     0.3
    Sep         394    13.1          9     0.3          9     0.3
    Oct         555    17.9          0     0.0          7     0.2
    Nov         432    14.4         57     1.9        400    13.3
    Dec         516    16.6        169     5.5        729    23.5
    Jan 2002    595    19.2          5     0.2        363    11.7
    Feb         532    19.0          4     0.1        157     5.6
    Mar         504    16.3          1     0.0        191     6.2
    Apr         310    10.3          7     0.2         63     2.1
    May         431    13.9          8     0.3         53     1.7
    Jun         429    14.3         41     1.4         45     1.5
    Jul         445    14.4        181     5.8         92     3.0
     Aug         455    14.7         91     2.9         32     1.0
    Sep         509    17.0        184     6.1        140     4.7
    Oct         322    10.4        219     7.1         62     2.0
    Nov         295     9.8        142     4.7         64     2.1
    Dec         233     9.0        120     4.6         48     1.5

    Date       Tornillo           Total earthquakes
               Total Daily avg.   Total Daily avg.

    Jan 2001      0     0.0        354    11.4
    Feb           0     0.0        189     6.8
    Mar           0     0.0        320    10.3
    Apr           0     0.0        306    10.2
    May           0     0.0        248     8.0
    Jun           0     0.0        307    10.2
    Jul           0     0.0        273     8.8
    Aug           0     0.0        250     8.1
    Sep           0     0.0        412    13.7
    Oct           0     0.0        562    18.1
    Nov           4     0.1        893    29.8
    Dec           0     0.0       1423    45.9
    Jan 2002      3     0.1        966    31.2
    Feb           0     0.0        693    24.8
    Mar           0     0.0        696    22.5
    Apr           0     0.0        380    12.7
    May           0     0.0        453    14.6
    Jun           3     0.1        474    15.8
    Jul           2     0.1        720    23.2
    Aug          12     0.4        590    19.0
    Sep          19     0.6        852    28.4
    Oct          13     0.4        616    19.9

    Nov           2     0.1        503    16.8
    Dec           1     0.0        402    16.1

Seismic activity of Cotopaxi in 2001 and 2002.²

The following is a summarizing history of Cotopaxi's activity from the year 1900 to 1942 (the last year of a suspected eruption), taken from the Smithsonian Volcanology Website.²There have been no confirmed eruptions since 1940.

Start Date: 1942 Feb 17 Stop Date: 1942 Feb 19

Eruption is UNCERTAIN

Volcanic Explosivity Index (VEI): 3?

Area of Activity: (press reports not confirmed)

Eruptive Characteristics:
    Central vent eruption
    Explosive eruption
    Damage (land, property, etc.)

Start Date: 1940 Stop Date: Unknown