Thanks for the comments. Other factors I was looking at were:
Effects on the US population which was at the time still concentrated on or near the coasts.
Effects on coastal agricultural land poisoned by sea water.
Effects on coastal cities like Boston, New York, Philidelphia, Washington DC, Charleston, Savannah, even down Florida to Havana and the Caribbean.
Effects on Florida.
Megatsunamis can be hundreds of feet high and several miles wide. Imagine the scene:
La Palma blows on August 23, 1812, megatsunami reaches the East Coast just as the British are taking and burning Washington DC on August 24. Suddenly, all the waters start draining out of the bays dragging ships and boats out to sea. Then, on the horizon, coming at high speed, is a 200 foot high wall of water at least a mile in width and extending all the way from north to south.