Can I juxtapose two clauses that share one object?

Solution 1:

Your sentence was:

1. Meltwater of the glaciers, especially outbursts of glacier-dammed lakes and moraine-dammed lakes, provide deluges of water, and glacial outwash provides abundant loose material, for debris flows.

You need to isolate each heavy syntactic element and then think of alternate ways of expressing the same idea that make the syntax of such a long sentence easier on your reader. This is a word-salad whose syntax is dubious and confusing at best:

C1: (meltwater (of the glaciers))
    (especially outbursts of (glacier-dammed lakes and moraine-dammed lakes))
    (provides)
    (deluges of water)

and

C2:  (glacial outwash)
     (provides)
     (abundant loose material)

Adj: (for (debris flows))

You don't want "C1 and C2 for debris flows", because that doesn't make sound grammatical sense, and also because loose material for debris flows is a garden-path collocation that leads your reader to misparse your sentence.

Trimming the extra bits, the key elements of your sentence work out to:

2. Meltwater *provide deluges and outwash provides loose material for debris flows.

The first verb provide is in the wrong number because its subject is meltwater. The verb should therefore be the singular provides, but that's the least of your troubles.

Your sentence contains neither a compound verb nor a compound subject, and making your two clauses sharing the same adjunct is a different kettle of fish.

Clause One

• subject: meltwater
• verb: provides
• object: deluges

Clause Two

• subject: outwash
• verb: provides
• object: material

The only thing those two independent clauses share in common is their verb, but it has not been reduced as you would with a compound subject. That's because the first subject goes with the first object, and the second subject goes with the second object.

The syntactic element you are trying to make apply to both those two clauses is the adjunct for debris flows. That is not the direct object. If you move the shared element to the start of the sentence, this becomes clearer:

3. For debris flow, meltwater provides deluges and outwash provides material.

Stylistically it is possible — but not always expedient — to factor out the second verb:

4. For debris flow, meltwater provides the deluges and outwash the material.

This sort of thing only works when the elements are light (short) the way I've outlined them here. Longer, heavier elements will lose the reader.

If we start putting back your extra element, the reader becomes lost. But we should fix what you have there first. Your parenthetical

• especially outbursts of glacier-dammed lakes and moraine-dammed lakes,

should be reduced because the duplication is too plodding. You have two choices, of which I prefer the second.

• especially outbursts of glacier- and moraine-dammed lakes,
• especially outbursts of lakes dammed by glaciers and moraines,

I also think those should be from not of:

• especially outbursts from lakes dammed by glaciers and moraines,

Be careful when adding back the material I've omitted in the previous focused solutions lest your reader become lost or bored. Your sentence as originally written is much too complicated to hold the reader's attention. Many readers will lose track of just exactly what's doing what to what, and to what purpose.

Try switching around the order of these individual constituents. Consider using nonfinite clauses via participles or infinitives to enliven the structure so your reader doesn't get bored with repetitive grammatical constructions. There's more than one way to skin a cat; here follow only a few of many possible ways:

6. Glacial meltwater, especially when released suddenly in outbursts from lakes dammed by glaciers and moraines, combines with the loose material from glacial outwash to provide for debris flows.

7. Glacial meltwater, particularly meltwater released in a sudden outburst from lakes whose glacial or moraine dams fail, combines with loose material from glacial outwash to provide debris flows.

8. Glacial meltwater, particularly meltwater released in a sudden outburst from lakes whose glacial or moraine dams fail, combines with loose material from glacial outwash to create debris flows.

9. Debris flows are provided for by glacial meltwater, especially if released suddenly from lakes previously dammed by glaciers and moraines, combining with the loose material of glacial outwash.

10. Debris flows are created when glacial meltwater, especially if released as a sudden outburst from lakes previously dammed by glaciers and moraines, combines with loose material from glacial outwash.

But seriously consider using more than one sentence: the use of a full stop (aka a period) should not be considered a moral failure by the writer. Rather, think of it as a kindness towards the reader.