In a small bowl mix together 1 1/2 cups crushed gingersnaps and 1 tablespoon sugar. Stir in melted butter or margarine. Press mixture evenly into a 9 inch pie plate. Bake for 15 minutes. Allow to cool.
In a medium bowl, combine pumpkin, 1 cup sugar, salt, ginger, cinnamon, and nutmeg. Stir until thoroughly mixed. Fold in whipped topping.
Spread ice cream in an even layer in bottom of cooled gingersnap crust. Pour pumpkin mixture over ice cream. Freeze at least 2 hours before serving. Garnish with whipped topping and crushed gingersnaps if desired.