Alahar is choose one:
a. a lava lake in a summit crater.
b. a volcanic mudflow that resembles fluid concrete.
c. a collapsed volcanic structure.
d. a glowing cloud of pyroclastic fragments and hot gas.

B. a volcanic mudflow that resembles fluid concrete.

Explanation:

Lahar -

Lahar is a form of debris or mud , basically made up of water , rocky debris and slurry .

Lahar are very devastating in nature as it flows out from the volcano along the river .

The characterstics of Lahar is , it is very large , and dense and viscous in nature .

One of the example if Lahar is ,

The Osceola Lahar , originated from the volcano of Mount Rainer in United states , specifically in the aresa of Washington , it covered the area of about 330 square kilometres , with a volume of about 2.3 cubic kilometres .

the answer is "c" im pretty sure.