Like Type II bursts, Type IIIs also drift from high to low frequencies and are widely attributed to the plasma emission mechanism. However, Type III bursts drift much more rapidly, around 100 MHz per second, and must therefore be related to disturbances that move more quickly than the shock waves responsible for Type IIs. Type III bursts are associated with electrons beams that are accelerated to small fractions of light speed ( ≈ ≈ 0.1 to 0.3 c) by magnetic reconnection, the process responsible for solar flares. In the image below, the chain of color contours show the locations of three Type III bursts at different frequencies. The progression from violet to red corresponds to the trajectories of electron beams moving away from the Sun and exciting lower and lower frequency plasma emission as they encounter lower and lower densities. Given that they are ultimately caused by magnetic reconnection, Type IIIs are strongly associated with X-ray flares and are indeed observed during nearly all large flares. However, small-to-moderate X-ray flares do not always exhibit Type III bursts and vice versa due to the somewhat different conditions that are required for the high- and low-energy emission to be produced and observed.