Final answer:
The channeled scablands topography of southeastern Washington was formed by tectonic plate movement and volcanic eruptions.
Step-by-step explanation:
The channeled scablands topography of southeastern Washington was formed by tectonic plate movement and volcanic eruptions. The younger terrain in the region was shaped by tectonic and volcanic forces, including crustal cracking, compression of the crust forming mountain ranges, and splitting of older impact craters. Additionally, the region experienced major volcanic eruptions, such as the eruption of Mount St. Helens in 1980, which caused significant changes to the landscape.