  For the first time, we demonstrate how an MHD avalanche might occur in a
multi-threaded coronal loop. Considering 23 non-potential magnetic threads
within a loop, we use 3D MHD simulations to show that only one thread needs to
be unstable in order to start an avalanche even when the others are below
marginal stability. This has significant implications for coronal heating in
that it provides for energy dissipation with a trigger mechanism. The
instability of the unstable thread follows the evolution determined in many
earlier investigations. However, once one stable thread is disrupted, it
coalesces with a neighbouring thread and this process disrupts other nearby
threads. Coalescence with these disrupted threads then occurs leading to the
disruption of yet more threads as the avalanche develops. Magnetic energy is
released in discrete bursts as the surrounding stable threads are disrupted.
The volume integrated heating, as a function of time, shows short spikes
suggesting that the temporal form of the heating is more like that of
\textit{nanoflares} than of constant heating.
