Polka in the 19th century also wrote many polkas to satisfy the demands of the dance-music-loving Viennese. In France, another dance-music composer Emile Waldteufel also wrote many polkas in addition to his chief profession of penning waltzes. The polka evolved during the same period into different styles and tempi. In principle, the polka written in the 19th century has a 4-theme structure; themes 1A and 1B as well as a 'Trio' section of a further 2 themes. The 'Trio' usually has an 'Intrada' to form a break between the two sections. The feminine and graceful 'French polka' (polka française) is slower
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