Complex sentence: The unstable lava formation of The Barrier has in the past unleashed several debris flows in the area below Garibaldi Lake, most recently in 1855-1856 forming a large boulder field which gives Rubble Creek its name.
Split into simpler sentences: The unstable lava formation of The Barrier has in the past unleashed several debris flows in the area below Garibaldi Lake. The most recent major landslide in 1855-1856 formed a large boulder field which gives Rubble Creek its name.