Hoé-soaⁿ sī 1 chióng tē-chit (geology) téng-koân leh kóng ê tē-hêng (landform), toā-hūn sī he̍k-chheⁿ ê hoé-chiuⁿ (magma) po̍k-hoat liáu-aū chō-chiâⁿ--ê. Tiàm-tī Bo̍k-chheⁿ, Thó͘-chheⁿ, Hái-ông-chheⁿ ê oē-chheⁿ mā ū 1 chióng peng-hoé-soaⁿ (ice volcano). Lēng-goā koh ū 1 chióng làm-hoé-soaⁿ (mud volcano). Tē-kiû ê hoé-soaⁿ tiāⁿ tiàm-tī tē-khak ê tē-pang (crustal plate) khah lím ê só͘-chāi. M̄-koh ū koá hoé-soaⁿ sī tiàm-tī tē-pang khah lāi-té-bīn hō-chò sio-tiám (hotspot) ê só͘-chāi; chit khoán hoé-soaⁿ tī Thài-iông-hē pa̍t-ê chio̍h-thaû-hêng he̍k-chheⁿ (rocky planet) kap oē-chheⁿ mā khoàⁿ ē tio̍h.

Ìn-nî Java-tó ê Bromo kap Semeru (aū-piah) hoé-soaⁿ teh chhèng-ian.