CREATE TABLE table_19622 ("Explosion" TEXT, "Location" TEXT, "Date" TEXT, "Yield  ( approximate ) " TEXT, "Altitude  ( km ) " TEXT, "Nation of Origin" TEXT)

What was the altitude of the yield of 1.4 megatons?
SELECT "Altitude (km)" FROM table_19622 WHERE "Yield (approximate)" = '1.4 megatons'
SELECT "Altitude (km)" FROM "table_19622" WHERE "Yield (approximate)" = '1.4 megatons'