Cagua - the less understood volcano

Cagua volcano is probably new to your hearing. Never heard before but yes, there is a volcano called Cagua.

Cagua volcano is a stratovolcano located in the north-east end of Luzon Island and is part of a 1,200 km-long volcanic chain, associated with eastward subduction along Manila Trench (Barrier et al., 1991). In the last 1.5 million years, the volcano has had three eruptive phases (Defant et al., 1989). The earliest phase generated calc-alkaline basaltic andesite and basaltic lavas. This was followed at 0.6 to 0.3 Ma, by deposition of thick andesitic ignimbrite deposit that covered the entire volcanic edifice. Most recent eruption was in 1860 and this was characterized by A phreatomagmatic eruption that produced thick pyroclastic flows (Defant et al., 1989).

Thermal manifestations in Cagua volcano is confined within <10 km radius from the crater over an area of 82 km2 at elevations ranging from 25 to 900 m above sea level. These manifestations include hot springs emanating from the flanks of the volcano and boiling mud pools that are mostly concentrated in the two solfatara areas at the crater of the volcano.

The team headed for Gonzaga, Cagayan Valley last 07-13 August 2016. The team was composed of PHIVOLCS staff headed by Raymond Maximo and ULB researchers headed by Prof. Alain Bernard.Samples were collected between 09 and 11 August 2016. Other dates were allocated for travel, administrative (courtesy call to LGU), and logistical arrangements in the study area.

09 August 2016

Water samples were collected from a bubbling cold spring (Fig. 1) in Brgy. Magrafil, Gonzaga, Cagayan Valley. Locals know the area as Site B. The pH of the spring was 7.0 (using pH paper). There was a strong sulfur smell around the vicinity of the sampling area and white deposits have formed within the rocks that surround the bubbling area. The cold spring was at an elevation of 401 m asl.

Next set of samples was collected from Napudot, also in Brgy. Magrafil, Gonzaga, Cagayan Valley. The place was called Napudot because of the hot water flowing out of the ground. The temperature of the spring was recorded by a thermocouple at 46.5°C and pH was about 6.0 (using pH paper). The eleveation of the spring is 280 m asl.

The last stop of the day was at Brgy. Tapel, Gonzaga, Cagayan Valley. This stop featured a cold spring. Samples were collected from this cold spring. The temperature wasn’t recorded but pH was measured at 5.0. The elevation of the spring is at 80 m asl.

10 August 2016

The team started the ascent to the crater at 7am and reached the northwest rim little past 8am. The elevation on the crater rim was recorded by a handheld GPS at 942 m asl. Solfatara area was about 100 m below the edge of the crater rim.

Samples were collected from the solfatara area for laboratory analysis. These water samples were heavily loaded with sediments. Temperatures of the mud pools were measured at 90.2°C. Some hot springs in the area were cooler with average temperature of 60°C. The pH of the water was between 1.0-2.0.

Deposits of sulfur were observed within the crater (Fig. 6). These deposits were specifically found in the active zone and around steaming vents and fumaroles. Fragments of sulfur were also found mixed with altered volcanic rocks. Some of the sulfur appeared to coat volcanic debris and boulders. Native sulfur was observed in several mud pools and it occurred as black liquid floating on top of the mud pool (Fig. 5c).

Southwest of this fumarole was the smaller solfatara area. The area was characterized by altered ground almost similar to the bigger solfatara area in the northeast. The ground was littered with altered volcanic rocks. Strong sound was emanating from these vents. Considerable amount of smokes rises from these fumaroles and vents.

11 August 2016

The hot springs north of the volcano were the target for the last day of this fieldwork. These were found in Sitio Manaring, Brgy. Cabiraoan and Brgy. San Jose, Gonzaga, Cagayan Valley. The Sitio Manaring hot springs were on the periphery of a flowing river. The temperature of water ranges from 64°C – 66°C. The small boulders around this area were partially covered with white deposits. The pH of the water was between 6.0 and 7.0 as tested using the pH paper. Elevation was recorded at 67 m asl (Fig. 7).

The sampling site in Brgy. San Jose was a make shift water well where locals probably have used for bathing or doing laundry. As seen from the picture, the well where the water samples were taken from was constructed to store the water coming from the ground. The temperature was about 41.7°C and pH was between 6-7 (Fig. 8).

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