OVSICORI-UNA reported that during September, Laguna Caliente, a summit lake of Poás, was mostly gray in color and produced gas columns that reached the craterrim. The level of the lake had dropped 5 cm with respect to August measurements and had a temperature of 46 degrees Celsius. On 25 October, a phreatic eruption produced a plume that drifted 12 km SW of the crater. Fumarolic activity from a pyroclastic cone on the floor of the crater produced gas plumes that drifted Wand SW. New points of gas discharge were noted from the crater floor, the SE and NE crater walls, the N terrace, and the NE edge of the crater.

On 26 September at least two phreatic eruptions occurred at Poás.
One during the night of 25 September reached a height of at least 350 m above the warm acid lake, depositing rock fragments, mud, and water in the southern part of the inner crater and outside the western part of the crater. '
Material ejected that night reached Trojas de Sarchí, almost 10 km SW.
A smaller eruption on the morning of 26 September was limited to the area of the lake, and formed green-yellow semicircular zones of mud and sulfur up to 75 m in diameter.

On 1 April, scientists visited Poás volcano and confirmed that Laguna Caliente at the volcano's summit had widened, and that sediments and blocks fromthe lake's bottom and surrounding walls were ejected during the explosions on 24-26 March 2006. The lava dome's (or pyroclastic cone's) N wall was greatly fractured and a 40 x 7 x8 m segment of the wall was gone. In addition, a 40 x 4 x 6 m chunk of the SE wall of the lake was missing and must have been destroyed during the explosions. They also found that the lake was light gray due to large quantities of suspended sediments, had a temperature of 54 degrees Celsius, had a pH of 0.63, and the lake level had decreased in comparison to the level before the explosions.

Seismicity decreased at Poás volcano by 27 March, 2006. Harmonic tremor that was recorded during the recent heightened activity ceased. As of the 27th, no significant deformation was recorded at the volcano and abundant evaporation continued at Caliente Lake.

Small phreatic eruptions began at Poás on 24 March 2006. The eruptions originated from the bottom of the volcano's Caliente Lake. Witnesses described a sudden emission of water and sediments S of the lake. Roaring was heard in a nearby tourist area and weak earthquakes were felt.
OVSICORI-UNA visited the E side of the volcano on 25 March and confirmed that water, blocks, and sediments from the bottom of the lake had been ejected.Several dozens of impact craters were seen with diameters between 15 and 60 cm, extending E as far as 700 m. Blocks were found that ranged in diameter from a few to 50 cm wide. During 22-27 March, harmonic tremor was recorded. On the 27th, there was a reduction in seismicity and it returned to normal levels. No deformation was measured at the volcano. A news article reported that the area around the volcano was closed to visitors.

Poás volcano erupted after 12 years of dormancy with two small steam and ash eruptions on 25th of March 2006 from the crater lake known as Laguna Calients. Authorities consider closing the easy-to-access crater rim to the public.