Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions contain juvenile (magmatic) clasts. It is common for a large explosive eruption to have magmatic and phreatomagmatic components.
The Aleipata Islands are a group of four uninhabited islands off the eastern end of Upolu Island, Samoa, in central South Pacific Ocean. The islands are eroded volcanic tuff rings, and consist of a small northern pair on Upolu's barrier reef, and a larger southern pair outside it. Collectively the islands have an area of about 1.7 km (0.66 sq mi). Administratively, the islands are part of the Atua district. The islands are important for Samoa's biodiversity and are protected by the Aleipata Marine Protected Area.
Nuʻutele is an island that consists of a volcanic tuff ring. It lies 1.3 km off the eastern end of Upolu island, Samoa, in central South Pacific Ocean. It is the largest of the four Aleipata Islands, with an area of 1.15 km (0.44 sq mi).
Nuʻutele, together with Nuʻulua, a smaller island in the Aleipata group, are significant conservation areas for native species of bird life. Nuʻutele features steep terrain, with vertical marine cliffs up to 180 m high.
Fanuatapu, an uninhabited island, is a volcanic tuff ring off the eastern tip of Upolu Island, Samoa, in central South Pacific Ocean. It is the smallest and easternmost of the four Aleipata Islands, with an area of 15 hectares. It has an automated lighthouse.
The Auckland volcanic field is an area of monogenetic volcanoes covered by much of the metropolitan area of Auckland, New Zealand's largest city, located in the North Island. The approximately 53 volcanoes in the field have produced a diverse array of maars (explosion craters), tuff rings, scoria cones, and lava flows. With the exception of Rangitoto, no volcano has erupted more than once, but the other eruptions lasted for various periods ranging from a few weeks to several years. Rangitoto erupted several times and recently twice; in an eruption that occurred about 600 years ago, followed by a second eruption approximately 50 years later. The field is fuelled entirely by basaltic magma, unlike the explosive subduction-driven volcanism in the central North Island, such as at Mount Ruapehu and Lake Taupō.
A monogenetic volcanic field is a type of volcanic field consisting of a group of small monogenetic volcanoes, each of which erupts only once, as opposed to polygenetic volcanoes, which erupt repeatedly over a period of time. The small monogenetic volcanoes of these fields are the most common subaerial volcanic landform.
Many monogenetic volcanoes are cinder cones, often with lava flows, such as Parícutin in the Michoacán-Guanajuato volcanic field, which erupted from 1943 to 1952. Some monogenetic volcanoes are small lava shields, such as Rangitoto Island in the Auckland volcanic field. Other monogenetic volcanoes are tuff rings or maars. A monogenetic field typically contains between ten and a hundred volcanoes. The Michoacán-Guanajuato field in Mexico contains more than a thousand volcanoes and is exceptionally large.