1. A volcano is a geological landform that consists of a vent or fissure in the Earth's surface through which molten rock, ash, and gases erupt.

2. Mt. Pinatubo's eruption in 1991 was considered as the second deadliest volcanic eruption of the 20th century due to the large amount of ash and volcanic debris it expelled, causing widespread damage and loss of life. Additionally, the eruption also caused a significant drop in global temperatures due to the ash and debris that was released into the atmosphere.

3. Lava is the term used to describe molten rock that has erupted from a volcano and cooled on the surface. Magma, on the other hand, is the term used to describe molten rock that is still beneath the surface.

4. Volcanoes are classified according to activity into three categories: active, dormant, and extinct. Active volcanoes are those that are currently erupting or showing signs of activity, dormant volcanoes are those that have not erupted in recent history but may do so in the future, and extinct volcanoes are those that are no longer active and will not erupt again.

5. The deadliest volcanic eruption of the 20th century is considered to be the eruption of Mount Tambora in 1815 which resulted in over 92,000 deaths.

Answer:

1.A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are diverging or converging, and most are found underwater.

2.The 1991 eruption of Mount Pinatubo in the Philippines' Luzon Volcanic Arc was the second-largest volcanic eruption of the 20th century, behind only the 1912 eruption of Novarupta in Alaska.

3.Scientists use the term magma for molten rock that is underground and lava for molten rock that breaks through the Earth's surface.

4.Volcanoes are classified as active, dormant, or extinct. Active volcanoes have a recent history of eruptions; they are likely to erupt again. Dormant volcanoes have not erupted for a very long time but may erupt at a future time. Extinct volcanoes are not expected to erupt in the future.

5.The ash and smoke cloud ejected by Mount Pinatubo in 1991 contained about twice as much matter as that thrown up by the El Chichón volcano (1982), making Pinatubo perhaps the largest eruption of the 20th century. Pinatubo erupted again in late August 1992, killing more than 72 people.

Explanation:

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