What exactly causes volcanoes to form?

Vol cano es form when mag ma , which is a mixture of mol ten rock , g ases , and sol ids , r ises from the Earth ' s mant le and cr ust to the surface . This process is called vol can ic activity . \n \n There are several types of vol cano es , including : \n \n 1 . Sh ield vol cano es : These are broad , g ently s lop ing vol cano es that form when la va flows slowly and stead ily from the vol cano . Sh ield vol cano es are often found in the Pacific Ocean . \n 2 . Compos ite vol cano es : These are t aller , ste eper vol cano es that are made up of multiple layers of la va and ash . Compos ite vol cano es can er upt explos ively , sending ash and de br is high into the air . \n 3 . C inder con es : These are small , con ical vol cano es that form when la va flows slowly and solid ifies at the surface . C inder con es are often found in areas where there is a lot of vol can ic activity . \n 4 . Super vol cano es : These are very large vol cano es that can produce massive er u ptions . Super vol cano es can produce ash and de br is that can blank et entire cities and regions . \n \n Vol cano es can form in different parts of the world , including at the mid - o cean ic rid ges , where new ocean ic cr ust is formed , and at sub du ction zones , where one t ect onic plate is sl iding beneath another . Vol cano es can also form in areas where there is a lot of mag ma in the Earth ' s mant le , such as in the Pacific Ocean . </s>