How many volcanoes have erupted and how long to they last? Many volcanoes are erupting as we speak and more than a thousand have erupted in the past 10,000 years. A volcanic eruption can last up to thousands of years. Scientists don’t have an accurate count of all the volcanoes, but there are about a thousand magma systems.
What causes them to erupt and what effect do they have on the earth and the people? A volcano erupts when the Earth’s plate tectonics shift. Lahar is fast flowing volcanic mudflow that is made up of ash and water. When a volcano erupts, it produces lots of rock and ash. This rock and ash is full of lots of minerals.