Learn Spanish (Latin America): Como el submarino se está sumergiendo muy rápido, suena la alarma. - Since the submarine is submerging very fast, the alarm is ringing.

When como starts a sentence to explain the reason for something, it translates to 'since' or 'because'. In this causal structure, it is followed by a normal indicative verb (like está here) because you are stating a known fact, not expressing doubt or emotion.

Why is there a se before está sumergiendo?

The verb here is sumergirse. While English just says the submarine 'is submerging', Spanish uses the pronoun se to show that the submarine is performing the action on itself (going underwater), rather than submerging some other object.

Could I attach the se to the end of the verb instead of putting it before está?

Yes! With the present progressive (está + gerund), you have two options. You can put the pronoun before the conjugated verb, as in this sentence, or attach it to the end of the gerund: está sumergiéndose. Just remember that if you attach it, you need to add an accent mark over the 'e' to keep the natural pronunciation.

Why is the word order suena la alarma instead of la alarma suena?

Both are perfectly correct! Spanish is much more flexible with word order than English. Putting the verb (suena) before the subject (la alarma) is a very common and natural way to emphasize the action or announce that a sudden event is happening.