Polka dances, which developed from Continental quadrilles, are danced to polkas. Introduced to Ireland in the late 19th century, there are today hundreds of Irish polka tunes, which are most frequently played on the fiddle or button accordion. The Irish polka is dance music form in , typically 32 bars in length and subdivided into four parts, each 8 bars in length and played AABB. Irish polkas are typically played fast, at over 130 bpm, and are typically played with an off-beat accent. The polka also migrated to the Nordic countries where it is known by a variety of names in
Types of volcanic eruptions Types of volcanic eruptions Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series. There are three different types of eruptions. The most well-observed are magmatic eruptions, which involve the decompression of gas within magma that