Final answer:
Milankovitch cycles, involving the Earth's orbital eccentricity, axial tilt, and precession, are responsible for the alternating cycles of glacial buildup and retreat over thousands to hundreds of thousands of years.
Step-by-step explanation:
The cycles of slow buildup and advance of glaciers followed by rapid shrinkage and retreat are caused by Milankovitch cycles, which include the eccentricity of the Earth's orbit around the Sun, the tilt of the Earth's axis, and the precession of the equinoxes. These orbital patterns have the most substantial effect on Earth's climate on time scales of thousands to hundreds of thousands of years. Changes in the shape of Earth's orbital path (eccentricity), the angle of Earth's rotational axis (obliquity), and the wobble of Earth's axis (precession) each contribute to the climatic patterns that drive glacier expansion and retreat.
Specifically, eccentricity affects how close Earth is to the Sun, while the tilt influences the distribution of solar radiation on Earth's surface. Precession, the slow conical motion of Earth's axis, is caused by gravitational forces and affects the timing of the seasons. Together, these cycles can either amplify or dampen climate changes, including those necessary for the onset and retreat of ice ages.