The magnetization of Pacific seamounts shows a surprisingly large variation when viewed as a function of time. Similar to normal upper oceanic crust, the basalts that form the external shell of volcanic seamounts have a high average magnetization immediately after formation. This high magnetization decays rapidly with time, resulting in a factor of 5 reduction in intensity in less than 500,000 years. Because submarine volcanoes appear to consist of the same basalts that form the upper part of the seafloor, low temperature oxidation of the magnetic mineral titanomagnetite is assumed to be responsible for the reduction in magnetization for both types of crust. Some large oceanic volcanoes are of sufficient volume that the upper capping rocks erupt subaerially and submerge completely due to thermal subsidence only after several million years. These capping rocks can be locally abundant (i.e., Hawaii), are exposed to a different post formation environment, and can have a magnetic mineralogy that is different from submarine volcanoes. In spite of these differences, the magnetization of subaerially erupted rocks of the Hawaii/Emperor Chain also may show a similar rapid reduction in intensity with age. Finally, seamounts of Cretaceous age show a factor of 2 higher average magnetization when compared to Tertiary seamounts, similar to the previously observed increased magnetization of Cretaceous seafloor basalts recovered from Deep Sea Drilling Project/Ocean Drilling Project cores. This increase in Cretaceous magnetization appears to be reflected in the increased amplitude of magnetic anomalies in some, but not all of the ocean basins, prior and subsequent to the Cretaceous Normal Superchron. The processes potentially responsible for the elevated Cretaceous magnetization values include a high geomagnetic field intensity, large-scale variations in whole rock major element geochemistry of the extrusive rocks, or a systematic acquisition of a secondary magnetization during the Cretaceous Normal Superchron. ¿ American Geophysical Union 1996