Irazu crater Lake

A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite. Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not made. Crater lakes covering active (fumarolic) volcanic vents are sometimes known as volcanic lakes, and the water within them is often acidic, saturated with volcanic gases, and cloudy with a strong greenish color. Lakes located in dormant or extinct volcanoes tend to have fresh water, and the water clarity in such lakes can be exceptional due to the lack of inflowing streams and sediment.

The Irazú Volcano (Spanish: Volcán Irazú) is an active volcano in Costa Rica, situated in the Cordillera Central close to the city of Cartago.

The name could come from either the combination of "ara" (point) and "tzu" (thunder) or a corruption of Iztarú, which was the name of an indigenous village on the flanks of the volcano. In Costa Rica it is known by the name of "El Coloso" (The Colossus) due to the catastrophes that it has provoked in the past.

The volcano's summit has several craters, one of which contains Diego de la Haya, a green crater lake of variable depth. It is the highest active volcano in Costa Rica. It is easily visited from San José, with a road leading right up to the summit craters and a weekly bus service to the top. It is thus a popular tourist spot. The volcano summit also spots a few television transmitters for television stations in San José.

From the top it is possible to see both the Atlantic and Pacific Oceans on a clear day. However, such clear days are very rare indeed, and it is typical for the volcano's summit to be covered in cloud for much of the time.