J. A. Darke 
Attack of the Mud Creatures [PDF ebook] 

After a mudslide devastates the neighbourhood of Winston Hills, no one expects it to get worse. When fifteen-year-old Greyson Bennell joins the volunteer cleanup effort, he thinks he’ll excavate some belongings and head home. But when his best friend Trevor goes missing, Grey starts to realize that the people around him are acting strangely . . . and it might have something to do with the mud that surrounds them.