Dekkið sprakk á veginum.

Dekkið is the definite form of dekk, meaning the tire rather than a tire.

• dekk = a tire / tire
• dekkið = the tire

The ending -ið is the definite article for a neuter singular noun in this form.

Dekk is a neuter noun.

That matters because Icelandic nouns change form depending on:

• gender
• number
• case
• whether they are definite or indefinite

So here:

• dekk = neuter singular indefinite
• dekkið = neuter singular definite

Sprakk is the past tense of the verb springa.

So:

• springa = to burst, to explode, to blow out
• sprakk = burst / blew out

It is a strong verb, so the vowel changes instead of just adding a regular ending.

A few useful forms:

• springa = infinitive
• sprengur = present tense, bursts
• sprakk = past tense, burst
• sprungið = past participle

Because á can take different cases depending on meaning.

Here it means location: on the road.
When á expresses location, it usually takes the dative.

• vegur = road (dictionary form)
• veginum = the road in the dative singular

So:

• á veginum = on the road

Then á would usually take the accusative instead of the dative.

Compare:

• á veginum = on the road / located on the road
• á veginn = onto the road / movement onto the road

So the case after á helps show whether something is in a place or moving to a place.

The dictionary form is vegur, which means road.

Its definite singular forms include:

• nominative: vegurinn = the road
• accusative: veginn
• dative: veginum
• genitive: vegarins

Since á here expresses location, Icelandic uses the dative, giving veginum.

Not necessarily. Springa can mean burst, blow out, explode, or rupture, depending on context.

With dekkið, the natural meaning is usually:

• the tire burst
• the tire blew out
• possibly the tire punctured, depending on context

So even though the verb can be dramatic in other contexts, here it is just the normal verb for a tire bursting.

This is a normal Icelandic main-clause pattern:

• Dekkið = subject
• sprakk = verb
• á veginum = adverbial phrase of place

Icelandic often follows verb-second word order in main clauses. In this sentence, the subject comes first, so the verb comes second.

You could also change the emphasis:

• Á veginum sprakk dekkið.

That still works, but then the place phrase is placed first for focus, and the verb still stays in second position.

A rough guide for an English speaker is:

• dekkið ≈ DEH-khyith

A few things to notice:

• e is like the e in bed
• kk in Icelandic is often pronounced with pre-aspiration, something like hk
• ð is like the th in this
• the ending -ið is not pronounced like English id

This is only an approximation, but it helps you avoid reading it like English deck-id.

A rough English-friendly approximation is:

DEH-khyith sprahk ow VEH-yih-nym

Very roughly, word by word:

• Dekkið ≈ DEH-khyith
• sprakk ≈ sprahk
• á ≈ ow
• veginum ≈ VEH-yih-num or VEH-yih-nym

A few pronunciation notes:

• á sounds like ow in cow
• g in veginum is not a hard English g
• unstressed syllables are often lighter than English speakers expect

Yes. Dekk is the normal word for a tire, especially in everyday contexts involving vehicles.

So Dekkið sprakk would naturally be understood as something like:

• The tire burst
• The tire blew out

If the context is a car, that is almost certainly how a native speaker would understand it.

Yes. In Icelandic, the definite article is usually attached to the end of the noun, not written as a separate word like English the.

So instead of a separate word, Icelandic often does this:

• dekk = tire
• dekkið = the tire

And:

• vegur = road
• vegurinn / veginn / veginum = different case forms of the road

This is one of the first big differences English speakers notice in Icelandic grammar.