You said the character can "increase his weight." By this I assume you mean he becomes more dense without increasing his size; he's still the same size as a human. Furthermore you said that he can become indestructible, so he's not going to break up on impact.
This means your character is not like a meteor hitting Earth, and not like a nuclear explosion, because he will not release all his energy at once on impact. Instead, he will punch a deep hole in the ground, gradually slowing over a distance of 70m to 300m as he passes through the rock. His kinetic energy will be released gradually along the length of this hole, and the blast radius on the surface will be fairly small. The impact will spray molten rock back up out of the hole.
In a collision at mach 50, the speeds and forces are so great that the tensile strength of the rock he is passing through doesn't matter very much. As a result, we can use Newton's approximation for the impact depth. We can assume he is passing through granite, with a density of 2.6 g/cm^3. The distance he travels through the granite depends on his orientation on impact. If he hits feet-first or head-first, then we might estimate his cross-sectional area to be 2 ft^2 (1860 cm^2), which means he will penetrate 300m deep. If he belly-flops, we might estimate his cross-sectional area to be 9 ft^2 (8360 cm^2), which means he will only penetrate 70m deep.
His impact energy will be about 2 * 10^13 J, or 5 kilotons TNT, which is about a third of the energy of the bomb dropped on Hiroshima. But it will not devastate nearly as large an area, because most of the energy will be dumped harmlessly deep underground.
It's difficult to say how much destruction there will be on the surface. For one thing it depends on his body orientation; head-first or feet-first will naturally result in a smaller crater. To truly answer this question we would need to do an appropriate fluid dynamics simulation. However, we can safely say the energy reaching the surface to cause damage will be only a small fraction of his initial kinetic energy. If we say that 10% of his initial kinetic energy is released as a surface blast, then we can use nukemap with an 0.5 kT detonation to get some idea of the damage: a crater 30m radius, 10m deep; a fireball 60m radius; heavy blast damage in 170m radius; moderate blast damage in 360m radius. Thermal radiation radius can be ignored, because the ground would act as a shield.
The real damage radius could be a lot less than this because what energy does reach the surface will be guided upwards by the shape of the hole, instead of spreading out horizontally.
There would also certainly be lava and rocks raining down from the sky in a large radius, but again, difficult to say what the radius of this effect would be without a fluid dynamics simulation.