Pre-caldera volcanism and topography The entire region has been deeply eroded by repeated
continental and alpine glaciations. No volcanic structures or rocks predating caldera collapse survived multiple glaciations and collapse of the caldera. However, the presence of volcanic rock fragments within the intracaldera tuff are evidence for pre-caldera volcanism, as are
dikes outside the caldera margin that have geochemical compositions distinct from rocks related to caldera collapse and later volcanism within the caldera.
First caldera collapse , pumice clasts flattened by compaction of hot pyroclastic flows. Around 4 million years ago large volumes rhyolitic
magma rose high into the crust. This intrusion most likely caused the surface to dome upwards. Fractures caused by this deformation may have provided conduits for some magma to reach the surface and erupt into relatively small volcanic structures such as felsic and intermediate
lava flows and
domes, cinder cones, and perhaps small
stratovolcanoes. Over 10s or 100s of thousands of years, this upward deformation eventually resulted in a semicircular fracture, or ring fault to form in the brittle crust.
The end of volcanic activity in the caldera (1.15 million years old), and the numerous vents in the Mount Baker Volcanic field, including the currently active
Mount Baker itself. == Comparison with other Cascades calderas ==