magic circle break

The magic circles on the walls and ceiling were probably to destroy the tunnel and bury
Kamijou alive. He knew that much. But that would mean circles on the floor weren’t
necessary. Destroying the floor wouldn’t help bury him.
(That means...that one circle means something else!)
Sherry Cromwell’s face blanched with surprise when she realized where he was headed.
She hastily swung her oil pastel and delivered commands to the nearby walls and pillars,
but she was too slow. Kamijou evaded the crumbling walls and slipped past the falling
pillars, thrust his hand toward the magic circle on the floor...
...And brought it down without a moment’s delay.
The magic circle shattered like a frozen raindrop.
That was the second spell Sherry had needed.
If it was to create a safe zone to protect her from the landslide...
Now that she had lost her protection, she could no longer be careless with the landslide.

- Toaru Majutsu no Index Volume 6, Chapter 4 Part 5