Cumulative upkeep—Pay 2 life. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
When Glacial Chasm enters, sacrifice a land.
Creatures you control can't attack.
Prevent all damage that would be dealt to you.
When Glacial Chasm's "enters" ability resolves, if you don't control any other lands, you must sacrifice Glacial Chasm itself.