What is the cause of the Chandler Wobble?

The cause of this wobble is believed to reside in the natural resonances in the body of the spinning earth due to the detailed distribution of mass in its surface, interior, oceans and atmosphere. This system has a '14-month' harmonic which can be excited through a complex pattern of forcings by the moon, sun and sudden crustal rearrangements (earthquakes). There are many distinct periodic excitations by the sun and moon and their changing distances and tidal forcings, and these result in distinct monthly, yearly and multi-year periodicities in the polar wander. The Chandler Wobble may be a natural harmonic resonance that is also stimulated by these other constant lunar-solar forcings at the natural resonance frequency of the solid earth.

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