how does a Cascadia type volcano erupt?

Answer 1

Look at my answer for this question: Explain why thick,sticky magma may cause a volcano to erupt explosively???

The Cascadian region is on the edge of a subduction zone. The oceanic plate is being pulled down under the continental plate. When the oceanic plate is pulled down, it takes water with it. Water lowers the melting point of rocks at depth; so once the water reaches the depth where rocks are on the verge of melting, it triggers the reaction. Since siliceous rocks melt at a lower temperature, and the continental crust has higher silica content than does the oceanic crust (oceanic crust is mafic), the magma formed is of a siliceous nature. The high silica content then gives the magma the ability to carry much of the water (in the form of a volatile) up to the surface with it.

Answer 2

I assume Cascadia refers to the geographical Area. This is a subduction zone. The material is ocean sediments being subducted and melted, fueling the volcano.
The material tends to be light andesite.
This type of material is very light and carries large amounts of superheated water and gasses.
When there is an eruption, the gas and superheated water greatly expand as they are not under pressure anymore.
This causes large, explosive type of eruptions. The superheated gasses and water cause large destructive mudflows. The ash is light and is blown high into the atmosphere.
A good example is the recent Mt St Helens eruption.

Answer 3

If logic wins over lateral thinking,.. I'd say that they simply 'dribble' their lava over the top and/or sides,.. ie cascading,.. here's more info for you too,.. hope this helps,.... http://vulcan.wr.usgs.gov/Volcanoes/Oregon/description_oregon_volcanoes.html