To date, the largest tsunami on record was on July 10, 1958, when a 7.7 magnitude earthquake from the Fairweather fault in southeast Alaska hit, ultimately causing a tsunami with a maximum height of 1,720 feet or 520 meters!
According to wsspc.org, the website for the Western States Seismic Policy Council out of Sacramento, California, the giant wave was caused when a 2400 x 3000 x 300 thick rock fell from the Lituya Glacier and landed 2,000 feet below in Lituya Bay that feeds into the Gulf of Alaska through a narrow inlet.
Even today, 60 years later, the damage done to the edges of the bay is still observable as all vegetation was destroyed by the wave and the land is still recovering.