A distorted guitar distorts the components of the power chord after mixing them. This means that you get intermodulation distortion between different notes. The sum and different tones generated by this distortion form a harmonic series when combined with the original notes.
A power chord is root + fifth, which is a 1:1.5 ratio of frequencies (exactly in just intonation, and very nearly in equal temperament). Intermodulation distortion produces tones of frequency ratio 1.5 + 1 and 1.5 - 1, giving 2 and 0.5. Combine them with the existing tones and you get 0.5:1:1.5:2. This is just the harmonic series 1:2:3:4, but pitched down an octave (all frequencies divided by two). A distorted power chord contains the harmonics of a single note pitched an octave lower, which is why it sounds "heavy".
There are many other harmonics in the notes, so the timbre is much more complicated that that, but the fundamentals are most prominent, so the distorted power chord sounds consonant.
And if you have a guitar with a hexaphonic pickup and distort each string individually you don't get intermodulation distortion between the notes, so you can play much more complicated chords without it sounding dissonant.
A power chord is root + fifth, which is a 1:1.5 ratio of frequencies (exactly in just intonation, and very nearly in equal temperament). Intermodulation distortion produces tones of frequency ratio 1.5 + 1 and 1.5 - 1, giving 2 and 0.5. Combine them with the existing tones and you get 0.5:1:1.5:2. This is just the harmonic series 1:2:3:4, but pitched down an octave (all frequencies divided by two). A distorted power chord contains the harmonics of a single note pitched an octave lower, which is why it sounds "heavy".
There are many other harmonics in the notes, so the timbre is much more complicated that that, but the fundamentals are most prominent, so the distorted power chord sounds consonant.
And if you have a guitar with a hexaphonic pickup and distort each string individually you don't get intermodulation distortion between the notes, so you can play much more complicated chords without it sounding dissonant.