I remember seeing a show on that. They figured out the wave height based on the tree line along the mountainsides (old v. new growth).
They went in immediately afterward and measured the maximum damage. The 1,700 plus was immediately across from the landslide, which was the second one there in a few years.
The landslide that happened in Glacier Bay earlier this year went unnoticed for days until a pilot flying near saw it. It was larger than the Lituya Bay slides.