Dacite in the context of Porphyritic

Santorini, officially Thira or Thera, is a Greek island in the southern Aegean Sea, about 200 km (120 mi) southeast from the mainland. It is the largest island of a small, circular archipelago formed by the Santorini caldera. It is the southernmost member of the Cyclades group of islands, with an area of approximately 73 km (28 sq mi) and a 2021 census population of 15,480. The municipality of Santorini includes the inhabited islands of Santorini and Therasia, and the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi, Anydros, and Christiana. The total land area is 91 km (35 sq mi). Santorini is part of the Thira regional unit.

Santorini is the most active volcanic centre in the South Aegean Volcanic Arc. The volcanic arc is approximately 500 km (300 mi) long and 20 to 40 km (12 to 25 mi) wide. The region first became volcanically active around 3–4 million years ago, though volcanism on Thera began around 2 million years ago with the extrusion of dacitic lavas from vents around Akrotiri. One of the largest volcanic eruptions in recorded history struck the island about 3,600 years ago, leaving a large water-filled caldera surrounded by deep volcanic ash deposits.

Nea Kameni is a small, uninhabited Greek island of volcanic origin located in the Aegean Sea, within the flooded Santorini caldera. Nea Kameni (new burnt) and the neighbouring small island Palea Kameni (old burnt) have formed over the past two millennia through repeated eruptions of dacite lava and ash. The Roman historian Cassius Dio records in the year 47 CE "This year a small islet, hitherto unknown, made an appearance close to the island of Thera." Cassius' report may refer to Palaia Kameni. Pliny the Elder reported the emergence of a new island on July 8, in the year of the consulship of M. Junius Silanus and L. Balbus, thus 19 CE.

Major eruptions over the past 300 years took place in 1707–1712, 1866–1870, 1925–1928, and 1939–1941. The last small eruption happened in 1950 and involved lava dome extrusion.

Palea Kameni, also known as Palia Kameni, is a volcanic island within the Santorini Caldera. The island was formed by a series of volcanic eruptions that formed large deposits of pumice and dacite lavas. The island's name translates to "Old Burnt Island".Palea Kameni is a private island, it was inhabited until it was bought in 1899 and sold in 1975.

A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions. Some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high to intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less viscous mafic magma. Extensive felsic lava flows are uncommon, but can travel as far as 8 kilometres (5 miles).

The term composite volcano is used because strata are usually mixed and uneven instead of neat layers. They are among the most common types of volcanoes; more than 700 stratovolcanoes have erupted lava during the Holocene Epoch (the last 11,700 years), and many older, now extinct, stratovolcanoes erupted lava as far back as Archean times. Stratovolcanoes are typically found in subduction zones but they also occur in other geological settings. Two examples of stratovolcanoes famous for catastrophic eruptions are Krakatoa in Indonesia (which erupted in 1883 claiming 36,000 lives) and Mount Vesuvius in Italy (which erupted in 79 A.D killing an estimated 2,000 people). In modern times, Mount St. Helens (1980) in Washington State, US, and Mount Pinatubo (1991) in the Philippines have erupted catastrophically, but with fewer deaths.

In volcanology, a lava dome is a circular, mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions on Earth form lava domes. The geochemistry of lava domes can vary from basalt (e.g. Semeru, 1946) to rhyolite (e.g. Chaiten, 2010) although the majority are of intermediate composition (such as Santiaguito, dacite-andesite, present day). The characteristic dome shape is attributed to high viscosity that prevents the lava from flowing very far. This high viscosity can be obtained in two ways: by high levels of silica in the magma, or by degassing of fluid magma. Since viscous basaltic and andesitic domes weather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite or dacite.

Existence of lava domes has been suggested for some domed structures on the Moon, Venus, and Mars, e.g. the Martian surface in the western part of Arcadia Planitia and within Terra Sirenum.

The tholeiitic magma series (/ˌθoʊleɪˈɪtɪk/) is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma into a more evolved, silica rich end member. Rock types of the tholeiitic magma series include tholeiitic basalt, ferro-basalt, tholeiitic basaltic andesite, tholeiitic andesite, dacite and rhyolite. The variety of basalt in the series was originally called tholeiite but the International Union of Geological Sciences recommends that tholeiitic basalt be used in preference to that term.

Tholeiitic rock types tend to be more enriched in iron and less enriched in magnesium and aluminium than calc-alkaline rock types. They are thought to form in a less oxidized environment than calc-alkaline rocks. Tholeiitic basalt is formed at mid-ocean ridges and makes up much of the oceanic crust. Almost all the basalt found on the Moon is tholeiitic basalt.

The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in magnesium and iron and produces rhyolite or granite. Calc-alkaline rocks are rich in alkaline earths (magnesia and calcium oxide) and alkali metals and make up a major part of the crust of the continents.

The diverse rock types in the calc-alkaline series include volcanic types such as basalt, andesite, dacite, rhyolite, and also their coarser-grained intrusive equivalents (gabbro, diorite, granodiorite, and granite). They do not include silica-undersaturated, alkalic, or peralkaline rocks.

Ignimbrite is a type of volcanic rock, consisting of a typically welded tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrounding atmosphere. New Zealand geologist Patrick Marshall (1869–1950) coined the term ignimbrite from the Latin igni- [fire] and imbri- [rain].

Ignimbrites are made of a very poorly sorted mixture of volcanic ash (or tuff when lithified) and pumice and/or scoria lapilli, commonly with scattered lithic fragments. The ash is composed of glass shards and crystal fragments. Ignimbrites may be fairly loose and unconsolidated, or a poor to strongly lithified (solidified) rock called lapilli tuff. Near the volcanic source, ignimbrites often contain thick accumulations of lithic blocks, and distally, many show meter-thick accumulations of rounded cobbles of pumice. Ignimbrites may be white, grey, pink, beige, brown, or black depending on their composition and density. Many pale ignimbrites are dacitic or rhyolitic. Darker-coloured ignimbrites may be densely welded volcanic glass or, less commonly, mafic in composition.

Ollagüe (Spanish pronunciation: [oˈʎaɣwe]) or Ullawi (Aymara: [uˈʎawi]) is a massive andesite stratovolcano in the Andes on the Bolivia–Chile border, within the Antofagasta Region of Chile and the Potosi Department of Bolivia. Part of the Central Volcanic Zone of the Andes, its highest summit is 5,868 metres (19,252 ft) above sea level and features a summit crater that opens to the south. The western rim of the summit crater is formed by a compound of lava domes, the youngest of which features a vigorous fumarole that is visible from afar.

Ollagüe is mostly of Pleistocene age. It started developing more than one million years ago, forming the so-called Vinta Loma and Santa Rosa series mostly of andesitic lava flows. A fault bisects the edifice and two large landslides occurred in relation to it. Later two groups of dacitic lava domes formed, Ch'aska Urqu on the southeastern slope and La Celosa on the northwestern. Another centre named La Poruñita formed at that time on the western foot of the volcano, but it is not clear whether it is part of the main Ollagüe system. Activity at the summit continued during this time, forming the El Azufre sequence.

Tomuraushi Volcanic Group (トムラウシ火山群, Tomuraushi-kazangun) is a volcanic group in Hokkaidō, Japan. Along with the Daisetsuzan Volcanic Group they make up the Ishikari Mountains in Daisetsuzan National Park. The group consists of andesite and dacite stratovolcanoes and lava domes.

Quilotoa (Spanish pronunciation: [kiloˈto.a]) is a water-filled crater lake and the most western volcano in the Ecuadorian Andes. The 3-kilometre (2 mi)-wide caldera was formed by the collapse of this dacite volcano following a catastrophic VEI-6 eruption about 800 years ago, which produced pyroclastic flows and lahars that reached the Pacific Ocean, and spread an airborne deposit of volcanic ash throughout the northern Andes. This last eruption followed a dormancy period of 14,000 years and is known as the 1280 Plinian eruption. The fourth (of seven) eruptive phase was phreatomagmatic, indicating that a Crater lake was already present at that time. The caldera has since accumulated a 250-metre-deep (820 ft) crater lake, which has a greenish color as a result of dissolved minerals. Fumaroles are found on the lake floor and hot springs occur on the eastern flank of the volcano.

Quilotoa is a site of growing popularity. The route to the "summit" (the small town of Quilotoa) is generally traveled by hired truck or bus from the town of Zumbahua 17 kilometres (11 mi) to the South, or more commonly by bus from Latacunga. Visitors have to pay two US dollars each to enter Quilotoa. There are a number of simple hostels in the immediate area offering services such as mules and guides. Activities include a four to five-hour hike around the caldera (whose diameter is just over 3 kilometres (2 mi)). The caldera rim is highly irregular and reaches its maximum elevations 3,810 metres (12,500 ft) to the N, 3,894 metres (12,776 ft) to the NW and 3,915 metres (12,844 ft) to the SE, at three lava domes. The 10-kilometre (6 mi) hike is sandy and steep in places and can be quite taxing, particularly if there is fog.

Kendrick Peak or Kendrick Mountain is one of the highest peaks in the San Francisco volcanic field north of the city of Flagstaff in the U.S. state of Arizona and is located on the Coconino Plateau in Coconino County.

Kendrick Peak rises to a height of 10,425 feet (3,178 m), which makes it the 11th or 12th tallest summit (depending on the source) in Arizona. Kendrick Peak is a lava dome between 2.7 and 1.4 million years old consisting primarily of dacite and rhyolite flows that were partly buried by andesite according to the USGS.

Raoul Island (Sunday Island; Māori: Rangitāhua) is the largest and northernmost of the main Kermadec Islands, 900 km (560 mi; 490 nmi) south south-west of 'Ata Island of Tonga and 1,100 km (680 mi; 590 nmi) north north-east of New Zealand's North Island. It has been the source of vigorous volcanic activity during the past several thousand years that was dominated by dacitic explosive eruptions, with the largest being VEI-6.

The area of the anvil-shaped island, including fringing islets and rocks mainly in the northeast, but also a few smaller ones in the southeast, is 29.38 km (11 sq mi). The highest elevation is Moumoukai Peak, at an elevation of 516 m (1,693 ft).

Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid cooling of lava relatively rich in silica and low in alkali metal oxides.