Changing the timeline causes it to, in simple terms, wobble (rather than simply veer off), as exhibited in Liang Oscillation. The study of this is called Liang Wave Theory. It is thought the shape of the 5th ‘Meta-dimension‘ is what determines the nature of this wave. The 5th Meta-Dimension is essentially a modelling of the change in spacetime (although not strictly a dimension as such). Spacetime’s “path” is determined by the varying warp of the fabric of spacetime, producing a sort of shape of probability. It is thought that this warping is what determines the largely unknown specifics of Quantum States.
Different effects (such as a time traveller’s presence) can change spacetime’s path, but curvature of the meta-dimension largely determines its overall path. Like a river meandering through the trough of least resistance, if it is diverted it will still follow the groove of the terrain. I won’t delve further into fourth and fifth dimensions just now; suffice to say it’s the realm within which the Liang effect manifests itself.
The other important thing to note about Liang oscillation is that on occasion changes can cause time to alter its event flow completely, almost ‘jumping out of the trough’ to a whole new path. This abrupt and permanent change is called a Liang Cascade, and although it remains only a theory, there is no possible way of proving if one has or hasn’t happened already. They are considered a Chrononaut’s worst-case-scenario, as a Liang Cascade will alter the future on an irrevocable, unrecognisable new course.