INSIVUMEH reported that on most days during 30 June-14 July the active lava dome of Santiaguito was visibly degassing and generating plumes rising up to ~3,000 m (10,000 ft) a.s.l. that tended to drift SW. Weak explosions with some rumbling sounds occurred during this time period and ashfall was reported in the high terrain of Parcelamiento Monte Claro (S) on 2 and 14 July. Explosions were observed on 5, 7, and 10 July that ejected incandescent tephra up to 50 m above the crater rim. The active lava flow front on the E flank was also a frequent source of incandescence that generated hot avalanches into the drainages of Nimá 1 (E) and San Isidro (SW). On 2 and 10 July slope failures were reported from the scarp remaining from the 9 May 2014 eruption.

On 15 July at 1430 lahars were triggered by heavy rainfall. INSIVUMEH reported that lahars were channelized within Nimá 1, San Isidro, and the tributaries of Samala. Seismic stations detected the flow; hot volcanic material dominated the lahars as well as tree trunks and branches and blocks 1-2 m in diameter. Vapor was rising from the lahars and there was a strong sulfur odor. INSIVUMEH extended the warning for the region, including the high bridge of Castillo Armas (on the international highway NE of San Sebastián) due to the convergence of several flows upstream from that site.

Geological Summary. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing E towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)