Learn Finnish: Tsunami iski vasta aamulla. - The tsunami didn't strike until the morning.

The adverb vasta means 'only' or 'not until' when referring to time. Finnish expresses this idea using an affirmative verb (iski) combined with vasta. English requires a negative structure ('didn't... until') to capture the exact same meaning naturally.

Could I translate 'until the morning' using a negative verb and the word 'ennen' instead?

Yes, but the grammar would change entirely. You could say Tsunami ei iskenyt ennen aamua (The tsunami didn't strike before the morning). However, using an affirmative verb with vasta is the most idiomatic way to express 'not until' in Finnish, and it is a structure you must master at this level.

Why do we use the adessive case ending -lla for aamulla (in the morning)?

When referring to general times of the day, Finnish uses the adessive case (-lla/-llä) to express 'in the' or 'at'. You will also see this pattern with words like illalla (in the evening), päivällä (during the day), and yöllä (at night).

What is the base form of iski, and why did it change this way?

Iski is the past tense (imperfect) of the Type 1 verb iskeä (to strike). To form the past tense, the final vowel -e of the stem is dropped and replaced by the past tense marker -i, resulting in the third-person singular form iski.