Both Yellowstone and Hawaiian volcanoes occur in the middle of tectonic plates, far from plate boundaries. Both are “powered” by what we call hotspots, anomalous areas of melting sourced deep within the earth. As it rises up, it burns its way through the tectonic plate and lava erupts onto the surface to form a volcano. As the tectonic plate moves, the volcano is carried away from the hotspot source, and the hotspot punches through again to create a new volcano. So for hotspots, you can follow a trail of volcanoes that gets older and older the farther you get from the hotspot. In Hawaii, this is a trail of old islands and seamounts that stretches all the way back to Russia and Kamchatka. In Yellowstone, we see that trail stretching across southern Idaho along the Snake River Plain. There are some important differences between Hawaiian volcanoes and Yellowstone. Hawai'i is on an oceanic plate, and that allows magma to rise more quickly. It has a basaltic composition with less silica and flows easily to build shield-shaped volcanoes. But Yellowstone is on a continental plate and the magma rises much more slowly. Eruptions are much less frequent, and the magma that's generated has a different composition. It is higher in silica and called rhyolite. Rhyolite has much more potential to erupt explosively. Because of the different tectonic settings (oceanic and continental), there are fluid and frequent eruptions in places like Hawai'i, and less frequent eruptions in a place like Yellowstone, with its sticky lava that can occasionally explode with extreme violence.