Volcanism that is initiated or occurs unrelated to an existing plate boundary is referred to as a hot spot . Hot spots are thought to be associated with narrow rising convection currents in the mantle called mantle plumes . In addition to the internal process of plate tectonics, Earth has a very active atmosphere which is driven by solar energy. This atmosphere is particularly effective because its temperature and pressure are close to the triple point of water so that water exist in all three phases as water, water vapor, and ice. Atmospheric processes tend to drive erosion and reduce topography.
Internal processes tend to raise topography.
Metallic hydrogen in Jupiter and Saturn can explain their relatively high densities with compositions dominated by hydrogen and helium, it can be the medium through which electric currents flow to form their strong magnetic fields, and its formation can release heat that is seem as the excess heat radiating from their surfaces. The formation of metallic hydrogen from molecular hydrogen is impeded by high temperatures, so as metallic hydrogen is formed deep in the planet, the heat produced by this metallic hydrogen production must be lost before more metallic hydrogen can be formed. This is called a negative feedback process and slows the process, causing metallic hydrogen to still be formed in Jupiter and Saturn today, and the process is still a significant generator of heat. The tilt of the spin axis of Uranus is thought to have been caused by an impact collision late in the formation of Uranus. However, its whole system of satellites is also similarly tilted, so either its moons were formed after tilting, or its moons were tidally reoriented.