Cumulative upkeep—Pay 2 life. When Glacial Chasm enters, sacrifice a land. Creatures you control can't attack. Prevent all damage that would be dealt to you.
You may choose not to untap Ice Floe during your untap step. {T}: Tap target creature without flying that's attacking you. It doesn't untap during its controller's untap step for as long as Ice Floe remains tapped.
Land Cap doesn't untap during your untap step if it has a depletion counter on it. At the beginning of your upkeep, remove a depletion counter from Land Cap. {T}: Add {W} or {U}. Put a depletion counter on Land Cap.
Lava Tubes doesn't untap during your untap step if it has a depletion counter on it. At the beginning of your upkeep, remove a depletion counter from Lava Tubes. {T}: Add {B} or {R}. Put a depletion counter on Lava Tubes.
River Delta doesn't untap during your untap step if it has a depletion counter on it. At the beginning of your upkeep, remove a depletion counter from River Delta. {T}: Add {U} or {B}. Put a depletion counter on River Delta.
Timberline Ridge doesn't untap during your untap step if it has a depletion counter on it. At the beginning of your upkeep, remove a depletion counter from Timberline Ridge. {T}: Add {R} or {G}. Put a depletion counter on Timberline Ridge.
Veldt doesn't untap during your untap step if it has a depletion counter on it. At the beginning of your upkeep, remove a depletion counter from Veldt. {T}: Add {G} or {W}. Put a depletion counter on Veldt.