Inside this caldera a new basaltic complex has grown from eruptions mainly on a semi-circular set of vents that include the Masaya and Nindiri cones.

Masaya continually emits large amounts of sulfur dioxide gas (from the active Santiago crater) and volcanologists study this (amongst other signs) to better understand the behavior of the volcano and also evaluate the impact of acid rain and the potential for health problems.

Although the recent activity of Masaya has largely been dominated by continuous degassing from an occasionally lava-filled pit crater, a number of discrete explosive events have occurred in the last 50 years.

The park has an area of 54 km2 (21 sq mi) and includes two volcanoes and five craters,[4] as well as a range of elevations between 100 and 630 meters above sea level.

An ophiolitic suite is found in the Nicoya Complex, which is made up of cherts, graywackes, tholeiitic pillow lavas and basaltic agglomerates.

This in turn passes north into the undeformed Tamarindo formation, a sequence of shallow marine, lacustrine and terrestrial sediments interspersed with ignimbrites.

Northeast of the Nicaraguan Depression, the Coyol and Matagalpa formations, run from Honduras to Costa Rica and still show evidence of some volcanic centres, distinguishable as constructional landforms.

Quaternary volcanic rocks are found mainly in the Nicaraguan Depression and form two major groups: the Marrabios and the Sierras formations.

The Marrabios Cordillera starts in the northwest with Cosiguina volcano and continues to the southeast with San Cristobal, Casitas, La Pelona, Telica and Rota.

The Hoyo, Monte Galan, Momotombo and Momotombito volcanoes are built upon ignimbrite deposits from the nearby Malpaisillo caldera.