While they collectively contain a lot of molten basalt (between 4,000 and 6,500 cubic kilometers of it), they are not very concentrated. Instead, these are often relatively small amounts of molten material that travels through cracks and fissures in solid rock. This keeps the concentration of molten material below the level required to enable explosions.
After the two streams of basalt material merge, they form a reservoir containing a large amount of molten crustal material, i.e. rhyolitic. The amount of rhyolite here is, at most, less than 500 cubic kilometers, so it could lead to a major eruption, albeit small by historical Yellowstone standards. But again, the proportion of molten material in this volume of rock is relatively low and is not considered likely to trigger eruptions.
From there to the surface, there are many distinguishing features. Relative to the hotspot, the North American plate above is moving westward, which historically means that the location of the eruptions has moved from west to east across the continent. Accordingly, there is an accumulation to the west of the bulk of near-surface magma that appears to be no longer connected to the rest of the system. It is small, with a volume of material of only about 100 cubic kilometers, and is too widespread to allow a major eruption to occur.
Future risks?
There is a similar near-surface bubble of molten material that may not currently be connected to the rest of the molten material to its south. It is smaller, probably less than 50 cubic kilometers of material. But it lies beneath a large mass of molten basalt, so it likely receives a fair amount of heat input. This location also appears to have fueled the caldera’s most recent major eruption. Therefore, while it could not lead to a major eruption today, it is not possible to rule out the location in the future.