Overwhelming amount
(Other definitions for tsunami that I've seen before include "Huge wave caused by earth tremor" , "Seismic sea wave" , "Great, fast-moving sea wave" , "High sea wave" , "Freak wave" .)
(Other definitions for avalanche that I've seen before include "frightening fall" , "Large snow or rock fall" , "Snowslip" , "Slide of large amounts of snow or stone" , "Great snowfall" .)
(Other definitions for plethora that I've seen before include "almost too much" , "Excess, glut" , "'Excess, superfluity (8)'" , "Abundant supply" , "Excessively large amount" .)