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Report on Guagua Pichincha (Ecuador) — March 2000

Bulletin of the Global Volcanism Network, vol. 25, no. 3 (March 2000)
Managing Editor: Richard Wunderman.

Guagua Pichincha (Ecuador) January-February marked by dome growth and small ash emissions

Please cite this report as:

Global Volcanism Program, 2000. Report on Guagua Pichincha (Ecuador). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 25:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200003-352020.

Volcano Profile |  Complete Bulletin


Guagua Pichincha

Ecuador

0.171°S, 78.598°W; summit elev. 4784 m

All times are local (unless otherwise noted)


This report covers the interval from 16 January to 28 February 2000 (table 10). This interval was marked by poor visibility and small emissions, some with and some without visible ash. These rose on the order of a few tens of meters to 2 km. Besides small ash emissions, evidence of the ongoing gradual growth of the dome (locally termed "dome 8") was provided by abundant rockfalls in the W crater, sulfurous odors, minor local ashfalls, and infrequent glimpses of extrusions and various changes within the crater. Several intervals of near-quiet also occurred.

Table 10. Seismic observations at Guagua Pichincha, 16 January-28 February 2000. The table shows the daily tally of these categories of earthquakes: long-period (LP), volcano-tectonic (VT), hybrid, rockfall, and emissions. Explosions were only recorded on 20 January (4) and 17 February (1). Dashes indicate a lack of (essentially zero) reported events. Courtesy of the Geophysical Institute.

Date LP VT Hybrid Rockfalls Emissions
16 Jan 2000 401 -- 10 136 5
17 Jan 2000 396 1 10 110 2
18 Jan 2000 330 -- 19 104 1
19 Jan 2000 65 7 24 6 2
20 Jan 2000 35 1 12 101 3
21 Jan 2000 108 1 6 79 1
22 Jan 2000 107 4 19 83 --
23 Jan 2000 82 -- 2 50 --
24 Jan 2000 50 2 21 40 2
25 Jan 2000 161 2 7 89 1
26 Jan 2000 202 4 21 86 1
27 Jan 2000 271 3 16 98 --
28 Jan 2000 271 3 16 98 --
29 Jan 2000 257 4 10 50 1
30 Jan 2000 105 18 11 19 1
31 Jan 2000 217 2 14 67 --
01 Feb 2000 107 -- -- 24 1
02 Feb 2000 116 2 7 65 --
03 Feb 2000 147 2 7 69 --
04 Feb 2000 163 1 9 42 --
05 Feb 2000 102 2 -- 21 --
06 Feb 2000 98 2 4 38 --
07 Feb 2000 100 -- 16 15 --
08 Feb 2000 124 1 4 39 --
11 Feb 2000 -- -- -- -- 1
12 Feb 2000 133 -- -- 15 2
13 Feb 2000 100 -- 12 63 2
14 Feb 2000 147 2 -- 45 8
15 Feb 2000 314 8 18 74 2
16 Feb 2000 421 1 10 95 2
17 Feb 2000 355 -- 4 80 6
18 Feb 2000 380 -- 21 97 5
19 Feb 2000 210 2 8 73 2
20 Feb 2000 80 2 -- 35 3
21 Feb 2000 283 2 -- 83 3
22 Feb 2000 233 -- 5 79 1
23 Feb 2000 253 5 5 80 2
24 Feb 2000 267 2 11 60 4
25 Feb 2000 276 1 -- 66 1
26 Feb 2000 210 5 7 52 4
27 Feb 2000 268 2 26 79 --
28 Feb 2000 401 1 98 87 1

The daily reports noted that small emissions occurred on many days in the reporting interval, which is also clear from the seismically based tallies shown on table 3. On the morning 19 January, the atmosphere was clear enough to see incandescent lava glowing through fractures in the dome. Observers noted lulls in fumarolic activity on 19 and 20 January, as well as on 22 and 23 January; in some cases they saw small, blue-tinged (sulfur-bearing) plumes that only rose 20-100 m. On 22 January observers looked into the small inner crater formed in 1999 (termed the "Herradura crater" or the "1999 crater") and noted a recent accumulation of fallen rocks there, including about twelve that stood ~10-12 m above the floor. Although the daily report noted that these rockfalls traveled in the direction of the head of the Río Cristal, their source was not made clear.

Starting at 1521 on 26 January a seismic emission signal with a small-to-moderate reduced displacement persisted for 120 minutes. Ash then fell W of the volcano. This emission followed a high-frequency seismic signal that possibly stemmed from a partial dome collapse. The possibility of a collapse appeared confirmed when observers noted the 26 January collapse of the crater's W zone. The latter event spawned a pyroclastic flow in the Río Cristal; associated deposits there exceeded 10 m in thickness.

In the morning on 1 February police reported the newly ash-covered Herradura crater generated white fumarolic columns that rose between 300 to 500 m. Blue vapors also hung in the air, indicating the presence of sulfur gases. On 2, 3, 12, 20, and on 28 February plumes rose to 1-2 km. In several cases the plumes carried noticeable ash, and a few ash falls were seen near the vent. The 12 February ash plume rose 1.3 km high; the plume's lower margins extended to engulf all sides of the caldera.

Geologic Background. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately to the W of Ecuador's capital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent in the breached caldera consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the central lava dome. One of Ecuador's most active volcanoes, it is the site of many minor eruptions since the beginning of the Spanish era. The largest historical eruption took place in 1660, when ash fell over a 1000 km radius, accumulating to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity, causing great economic losses.

Information Contacts: Geophysical Institute (Instituto Geofísico), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador.