  The presence of chaotic transients in a nonlinear dynamo is investigated
through numerical simulations of the 3D magnetohydrodynamic equations. By using
the kinetic helicity of the flow as a control parameter, a hysteretic blowout
bifurcation is conjectured to be responsible for the transition to dynamo,
leading to a sudden increase in the magnetic energy of the attractor. This
high-energy hydromagnetic attractor is suddenly destroyed in a boundary crisis
when the helicity is decreased. Both the blowout bifurcation and the boundary
crisis generate long chaotic transients that are due, respectively, to a
chaotic saddle and a relative chaotic attractor.
