What Causes Potholes? How Water, Traffic, and Winter Break Down Asphalt

Potholes seem to appear overnight, usually in late winter, usually in the worst possible spot. But the process that creates them has been running for months — sometimes years — before the pavement finally gives way.

What causes potholes is not complicated, and that is good news. Three ingredients are required, and removing any one of them stops the process. Understanding the sequence is the difference between reacting to potholes every spring and preventing most of them.

Key Takeaways

• Potholes require three things: water, a void or weakness in the pavement, and traffic load.

• Water is the root cause. It enters through cracks, saturates the base, and removes the support beneath the surface.

• Freeze-thaw cycles accelerate the process dramatically — southeastern Pennsylvania sees dozens each winter.

• Traffic delivers the final blow, flexing unsupported pavement until it fractures and breaks loose.

• Nearly every pothole starts as a crack that was left open, which is why crack sealing is the highest-return maintenance there is.
  

The Four-Stage Life of a Pothole

Stage 1: A crack opens

Every pothole begins with an opening. It might be a thermal crack from seasonal expansion and contraction, a joint that was never sealed, a fatigued area under repeated wheel loads, or simply a surface that has oxidized to the point of becoming porous.

At this stage the pavement is still fully functional. It is also, for the moment, cheap to fix.

Stage 2: Water gets underneath

Rain and snowmelt run into the crack and reach the aggregate base. Asphalt is designed to shed water, not hold it, and the base is designed to drain — but only if water arrives from above and leaves from below. Trapped water does neither.

Saturated base material loses its ability to carry load. The stone shifts, fine material washes away, and small voids form beneath a surface that still looks intact.

Stage 3: Freeze-thaw enlarges the void

This is where Pennsylvania's climate does real damage. Water expands roughly nine percent when it freezes, prying the crack wider and pushing base material apart. When it thaws, the material settles unevenly and more water enters.

Our region is particularly hard-hit because temperatures oscillate around freezing rather than staying frozen. Northern states with sustained deep cold often see fewer full cycles per season than we do. Each oscillation enlarges the void a little more.

Stage 4: Traffic breaks the surface

Now you have unsupported asphalt spanning a void, like a floorboard with a missing joist. Every vehicle flexes it. The asphalt fatigues, cracks through, and a chunk breaks free.

Once the hole is open, deterioration accelerates sharply. Tires pump water in and out under pressure, edges spall off, and what started as a hairline crack becomes a repair with a price tag.

The Contributing Factors

Factor	Role in Pothole Formation
Poor drainage	Standing water has time to penetrate; the single biggest controllable risk
Inadequate base	Thin or poorly compacted base fails under normal loads
Heavy vehicles	Delivery trucks and dumpsters concentrate load far beyond passenger cars
Age and oxidation	Older asphalt is brittle and porous, cracking more easily
Deferred crack sealing	Open cracks are the entry point for everything above
Utility cuts	Patched trenches are common failure points if backfill was poorly compacted

Early Warning Signs

Potholes announce themselves well before they form. Watch for:

Cracks wider than a quarter inch. Wide enough to admit meaningful water. These should be sealed before winter.

Alligator cracking. Interconnected cracks in a scaled pattern mean the base is already failing beneath that area. Potholes are the next stage.

Standing water. Any spot that holds water for more than an hour after rain is a future pothole location.

Depressions or dips. Subtle low spots indicate base material has already migrated.

Raveling. Loose aggregate and a gritty surface texture mean the binder has deteriorated and the surface is losing cohesion.

Edge crumbling. Edges have no lateral support and typically fail first.

How to Break the Cycle

Since water is the root cause, every effective strategy targets water.

Seal cracks before winter. This closes the entry point. It is inexpensive, fast, and prevents the great majority of pothole formation. Any crack wide enough for a coin should be filled before the first hard freeze.

Sealcoat on schedule. Sealcoating restores the surface barrier that UV exposure strips away, reducing absorption across the whole pavement rather than just at cracks. Every two to three years is the standard interval in this climate — our sealcoating and pavement maintenance page covers the timing.

Fix drainage. Correct low spots, redirect downspouts away from pavement, and keep edges clear so runoff has an exit.

Repair small defects immediately. A dip or a hairline network is cheap to address now and expensive to address after a winter.

Address recurring failures properly. If a pothole returns after patching, the base is the problem. Surface repairs will not hold, and full-depth asphalt repair is the solution.

Frequently Asked Questions

Why do potholes appear mostly in late winter and early spring? That is when the season's accumulated freeze-thaw damage meets saturated base conditions and continued traffic.

Can a pothole form without visible cracks first? Rarely in a sound pavement. Most trace back to a crack, joint, or utility cut — though the opening may have been small enough to overlook.

Does filling a pothole fix the underlying problem? Only if the repair reaches sound base. Surface-level fills over a failed base reopen within a season.

How quickly do potholes grow? Fast once open. A small hole can double in size within weeks under traffic and wet conditions.

Are potholes preventable? Largely, yes. Consistent crack sealing, sealcoating, and drainage maintenance prevent most of them.

Stop Them Before They Start

Potholes are the final stage of a process that gives you months of warning. Property owners who seal cracks each fall and keep water moving spend dramatically less on pavement over time than those who patch every spring.

HD Paving is licensed, insured, and warranties every job we complete across Montgomery County and the surrounding region. Contact us for a pre-winter assessment of your driveway or lot.