Adverbial Clauses

What Are Adverbial Clauses? 
An adverbial clause (or an adverb clause) is a group of words which plays the role of an adverb. (Like all clauses, an adverbial clause will contain a subject and a verb.)

For example:

Keep hitting the gong hourly.(normal adverb)
Keep hitting the gong until I tell you to stop.(adverbial clause)

In the examples above, the normal adverb and adverbial clause both tell us when the gong is to be hit. They are both adverbs of time. All adverbs (including adverbial clauses) can usually be categorized as one of the following:

Adverbs of Time:
An adverb of time states when something happens or how often. An adverb of time often starts with one of the following subordinating conjunctions:after, as, as long as, as soon as, before, no sooner than, since, until, when, or while. 

Here are some examples:

After the game has finished, the king and pawn go into the same box. (Italian Proverb)
I stopped believing in Santa Claus when my mother took me to see him in a department store, and he asked for my autograph. (Shirley Temple)
As soon as you trust yourself, you will know how to live.

Adverbs of Place
An adverb of place states where something happens. An adverb of place often starts with a preposition (e.g., in, on, near) or one of the following subordinating conjunctions: anywhere, everywhere, where, or wherever. 

Here are some examples:
In a world where there is so much to be done, I felt strongly impressed that there must be something for me to do. 
I am not afraid of the pen, the scaffold, or the sword. I will tell the truth wherever I please. (Mother Jones)

Adverbs of Manner
An adverb of manner states how something is done. An adverb of manner often starts with one of the following subordinating conjunctions: as, like, or the way. 

Here are some examples:
He acts like it is a joke.
We don't have conversations. You talk at me the way a teacher talks to a naughty student.
Except for an occasional heart attack, I feel as young as I ever did. (Robert Benchley)

Adverbs of Degree or Comparison
An adverb of degree states to what degree something is done or offers a comparison. An adverb of degree often starts with one of the following subordinating conjunctions: than, as...as, so...as, or the...the. 

Here are some examples:
He is as smart as he is tall.
She is not so bright as she thinks she is.

Adverbs of Condition:
An adverb of condition states the condition for the main idea to come into effect. An adverb of condition often starts with if or unless. 

Here are some examples:
If the facts don't fit the theory, change the facts. (Albert Einstein)
If the English language made any sense, a catastrophe would be an apostrophe with fur. (Doug Larson)

Adverbs of Contrast:
An adverb of contrast offers a statement which contrasts with the main idea. An adverb of contrast often starts with one of the following subordinating conjunctions: though, although, even though, while, whereas, or even if. 

Here are some examples:
Although golf was originally restricted to wealthy, overweight Protestants, today it's open to anybody who owns hideous clothing. (Dave Barry)
A loud voice cannot compete with a clear voice, even if it's a whisper. (Barry Neil Kaufman)

Adverbs of Reason:
An adverb of reason offers a reason for the main idea. An adverb of reason often starts with one of the following subordinating conjunctions: as,because, given, or since. 

Here are some examples:
I don't have a bank account, because I don't know my mother's maiden name. (Paula Poundstone)
Since you are like no other being ever created since the beginning of time, you are incomparable. (Brenda Ueland)

Properties of an Adverbial Clause:
Here are the properties of an adverbial clause:
-An adverbial clause is an adjunct. This means it can be removed without the sentence being grammatically wrong.
-An adverbial clause is a dependent clause. This means it cannot stand alone as meaningful sentence in its own right.
-An adverbial clause usually starts with a subordinating conjunction (e.g.,although, because, if, until, when)
-An adverbial clause will contain a subject and a verb. (This is what makes it a clause as opposed to a phrase.)

Taken from:

http://www.grammar-monster.com/glossary/adverbial_clauses.htm