From a point you can see, a wave of molten rock and flame surges out in a 10x20ft area. Everyone in the area must make a dec save of take 7D10 fire damage, pushed back 10ft and knocked prone. 

Dex save for 1/2 damage and no push or prone

Upcasting= 1D10 for every level above 5th and +5 ft length or width your choice