abysm
abyss
arroyo
box canyon
breach
break
canyon
cavity
chap
chasm
check
chimney
chink
cirque
cleft
cleuch
clough
col
combe
coombe
corrie
coulee
couloir
crack
cranny
crevasse
crevice
cut
defile
dell
dike
ditch
donga
draw
excavation
fault
fissure
flaw
flume
fracture
furrow
gap
gape
gash
gorge
groove
gulch
gulf
basin