Thesis (Ph.D., Geology)--University of Idaho, June 2014 | The thermal history of a rock can provide information about a process that is much larger than the rock itself. In this dissertation, I present three studied that evaluate a larger earth process that is illuminated by the speed and conditions of cooling or heating each rock type experienced. Chapter 1 looks at how a chemical boundary layer might form in the upper mantle due to the cooling path that hydrated cratonic lithosphere takes. I study this seismically-distinct layer using the geochemistry of xenoliths I retrieved from the online database, PetDB. Chapter 2 and 3 use the cooling history of volcanic products to evaluate surface processes. The second chapter illustrates how the cooling history of lithic and juvenile clasts in pyroclastic density currents reveal that boiling-over eruptions result in high air entrainment and a thermally heterogeneous deposit. The final chapter characterizes spatter, an explosive volcanic product, at Devil's Garden, OR and quantifies the accumulation and cooling rates required to produce spatter deposits.