“ The Mt St Helens lava dome gradually grow over the November 10, 2004 to February 28,2008 time period. Lava flows from Mt.St. Helens typically affects areas within range of 6 mi (10 km) of the vent.”information from http://volcanoes.usgs.gov/volcanoes/st_helens/st_helens_hazard_74.html
The lava dome changed by the lava dome sometimes getting bigger and sometimes getting smaller
This means that the lava dome recreated itself in a long period of time. And the lava flows from mt. st. helens traveled pretty far from the mountain. The north flank was creeping towards failing by the time may 18th had came. The ape cave is one of the numerous lava tubes formed in the caves basalt.
1980 Mt. St. Helens eruption April 15 had cryptodome, April 30 had even more cryptodome, may 15 had a lot more cryptodome. The cryptodome made a landslide when the cryptodome was exposed a lateral blast happened, further cryptodome exposure caused eruption column the eruption column went up for 9 hours, and the lateral blast went out to the side.
Information from the animated 1980 Mt St Helens buildup and eruption.