Thrash metal is generally characterized by high-speed riffs, rapid-fire drumming, and aggressive vocals. Metallica's Kill 'Em All and Slayer's Show No Mercy, both released in 1983, were arguably the first true thrash albums. Healthy thrash scenes sprouted in the USA, particularly the San Francisco area. In the mid to late eighties the thrash metal scene took a steep rise into public recognition, reached its peak in popularity by the end of the eighties, and then gradually faded.