At Minehead, Charles is in a terrible hole (5)
I believe the answer is:
chasm
'a terrible hole' is the definition.
'chasm' can be an answer for 'hole' (I have seen 'Deep hole' mean 'chasm' so perhaps 'hole' could also mean 'chasm'). I am unsure of the 'a terrible' bit.
'at minehead charles' is the wordplay.
'at' says to put letters next to each other.
'minehead' becomes 'm' (head letter of 'mine').
'charles' becomes 'Chas' (shortened form).
'm' after 'chas' is 'CHASM'.
'is in' acts as a link.
Can you help me to learn more?
(Other definitions for chasm that I've seen before include "Deep fissure; gulf" , "What's split" , "A deep opening in the earth" , "Pit" , "Wide gap" .)