Cobb hotspot

Over geologic time, the Earth's surface has migrated with respect to the hotspot through plate tectonics, creating the Cobb–Eickelberg Seamount chain.

The Cobb hotspot has created an underwater mountain range that extends 1,800 km (1,100 mi) to the northwest and ends at the Aleutian Trench.

The old, northwestern end of the chain collides with a subduction zone; therefore, the true age of the hotspot is difficult to determine as the oceanic crust is being consumed.

[3][4] The central ridge of the hotspot is thicker than the surrounding crust by a few kilometers and may be accumulated buildup from the magma released at the hotspot, which is essentially a submarine volcano with a root twenty to forty kilometres (12 to 25 mi) in diameter, reaching a depth of 11 kilometres (6.8 mi) beneath the volcano.

[10] It is inferred that much of the difference in basalt composition along the chain is due to the time-dependent distance between hotspot and ridge.

Therefore, as the Pacific plate migrated, the magma from the Cobb hotspot interacted with different thicknesses of crust.