how old is this chain?
The Emperor Seamounts is 81 million years.
Hawaiian–Emperor seamount chain
The oldest age for the Emperor Seamounts is 81 million years, and comes from Detroit Seamount. However, Meiji Guyot, located to the north of Detroit Seamount, is likely somewhat older.

when is the last time mauna kea erupted 6,000 to 4,000 years ago. who were the early settlers here? Ancient Hawaiians. what are a few of its geological features? It is the largest and youngest island of the Hawaiian–Emperor seamount chain and it is the fourth oldest and fourth most active volcano.
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Hawaiian–Emperor seamount chain [SEP] Formation
A look at the USGS map on the origin of the Hawaiian Islands clearly shows this "spearpoint". In a more recent study, Sharp and Clague (2006) interpret the bend as starting at about 50 million years ago. They also conclude that the bend formed from a "traditional" cause—a change in the direction of motion of the Pacific plate.