Ground frost, an extremely rare weather event in tropical countries like Costa Rica, was reported early Sunday at Irazú Volcano National Park.

Park rangers released a series of photos showing frost covering vegetation, trails and open areas near the summit of the volcano in Cartago Province. Rangers described the event as the start of the area’s “frost season,” when temperatures drop sharply in the highest elevations.

According to the National Meteorological Institute (IMN), the lowest temperature recorded at dawn Sunday at the volcano’s summit was about 41°F (5.2°C).

Frozen conditions may recur if temperatures drop to approximately 40°F (4°C) and a cold front moves across the country, IMN said. The cold front season in Central America typically runs from late November through March, with peak activity between December and February.

The National System of Conservation Areas (Sinac) notes that Irazú is Costa Rica’s highest volcano, rising 11,260 feet (3,432 meters) above sea level. Average annual temperatures at the summit range from 41°F (5°C) to 48°F (9°C). The volcano is a stratovolcano with an irregular subconical shape and five distinct craters.

Irazú Volcano National Park was established by Law No. 1917 on July 30, 1955. The name “Irazú” evolved from “Iztarú,” an Indigenous village located near the volcano. The original term meant “hill of tremor and thunder,” according to historical accounts.

The most recent eruption was recorded in 1994, when activity on the north wall of the main crater triggered an avalanche that slid into the Sucio River bed and reached beyond the river’s bridge on the Braulio Carrillo highway in Cartago. Since then, the volcano has only displayed fumarolic activity on the north wall of the main crater.

Irazú Volcano National Park opens to visitors at 8 a.m. Tickets can be purchased through Sinac’s website.

Sinac manages Costa Rica’s national parks and protected areas.

IMN is the government agency responsible for issuing weather forecasts, hazardous weather advisories and related public-safety information.