GMAT Sentence Correction (SC) | Re: According to a recent study, Earth's magnetic north pole is moving

According to a recent study, Earth's magnetic north pole is moving away from Alaska and toward Siberia so rapidly, within 50 years, that the swirling green auroras of the Northern Lights might be visible in cities as far south as Rome, which is located at 41º north latitude.

A. rapidly, within 50 years, that the swirling green auroras of the Northern Lights might be visible in cities as far south as Rome, whichis
The placement of that is inappropriate and because of which the 'within 50 years' makes no proper sense.