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There were several in the caldera but most were outside and of various sizes. The questions to be answered are, why the difference in size or magnitude and what causes the rhythm? Obviuosly the Mt itself and the large crator, I referred to as caldera because of its size, at the summit were created by greater forces than the smaller vents. The one I was standing on, at the time, rose 1500 feet above the rim of the caldera, and was the considerably taller than all of the rest and still growing.
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Now maybe I'm massively out on my knowledge of vulcanism here but I think what I'm about to say is generally accepted. I am under the impression that calderas form either;
When a massive pressure force is built causing a particularly violent eruption. This can be due to either a blockage in a volcanic vent or a high proportion of silica in the magma which triggers the rapid formation and expansion of gases as the magma nears the atmosphere, both of which can build massive pressure forces (much greater than distant transitting planets...). Such powerful eruptions effectively create a big gaping hole...a caldera? This pressure shouldn't require planetary interactions to build up by my thinking just accepted terrestrial processes. It equally need not be the case during every eruption, a vent may not become blocked or a new path may be found before such pressures have built and separate, less spectacular vents can be formed in the vicinity of the previous high energy vents.
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When a magma pocket becomes depleted creating a large subterranean cavern, as pressure in this cavern reduces with continued loss of magma through eruptions a point may eventually be reached where the pressure is no longer sufficient to support the rock above it and a collapse occurs. This fills the cavern and leaves a depression at the surface in the form of a caldera.
These are both events associated with vulcanism on various scales and should therefore be expected to be found in association with other volcanic features such as dormant and active volcanic vents. We need not invoke mysterious celestial forces to explain their existence in proximity to one another.
The fact that the particular vent you are speaking of was taller than the rest and still growing means very little. These large-scale events need not have occured very often, regularly or recently to leave long lasting marks on landscapes. The vent in question would appear to be the one/or one of several that is currently active, clearly it has not yet been blocked and/or it formed after the collapse of the main magma chamber and is erupting regularly and tamely to build its cone. This was likely the case with the other vents you could see before they became inactive for whatever reason (exhaustion of magma supply/transit of crust away from supply/blockage and re-routing of magma through a new vent...etc.) once they stopped building through regular eruptions bog standard weathering will have got to work on their benign forms and reduced their stature to the apparent insignificance you now note. Or they could have been involved in high impact events and their previous forms obscured by the creation of calderas and the like.
I really do not feel that planetary forces are needed to explain these phenomena, much as I do not believe they are required to explain the enhanced warming trend we are seeing on Earth.