According to IRD-IG, during 4-6 March Strombolian activity at Tungurahua was accompanied by gas emissions that reached 1-2 km above the volcano. Incandescent ejecta rose 50-200 m above the western crater rim, tephra fell around the crater, and blocks rolled down the volcano's upper flanks. On the 5th and 6th small amounts of fine ash fell to the NW in Patate Valley and in Ambato Valley. An explosion on the 6th at 1524 produced an ash cloud that rose 4 km above the crater and drifted to the N. During 7-9 March, volcanism was less intense. On the 10th volcanism increased; small amounts of ash fell on the volcano's W flank, and incandescent projections reached ~100 m above the crater. IG reported that on 12 March a gas plume, with little ash content, rose 2 km above the volcano and drifted to the W.

Geological Summary. Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II collapsed about 3,000 years ago and produced a large debris-avalanche deposit to the west. The modern glacier-capped stratovolcano (Tungurahua III) was constructed within the landslide scarp. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Sources: Institut de Recherche pour le Développement (IRD), Instituto Geofísico-Escuela Politécnica Nacional (IG), Washington Volcanic Ash Advisory Center (VAAC)