Most cracks in foundations comes from soil settlement and stress on the foundation walls. Concrete is a very sturdy building material. It lasts a very long time, but after it gets hard it can and often will crack.
Concrete foundation cracks will be either vertical or horizontal. Typically, small vertical cracks are not structural and most horizontal foundation cracks are.
The most common cause of horizontal cracks in a foundation is from soil pressure. The soil itself can expand, if it has a high clay content. However, most expansion of the soil and dirt around your house in Massachusetts is caused by the freezing and thawing process of the ground.
Your foundation wall should be acting as a retaining wall against the soil swell. A horizontal crack in a foundation wall is likely a sign that the foundation is failing under the pressure being exerted by the surrounding soil. The soil outside the foundation wall exerts an enormous pressure on the foundation wall. The weight of the house itself also exerts a lot of pressure on the foundation as well. Occasionally the combined pressures can cause horizontal cracks in the foundation wall.
The severity of the cracking and the effect they will have on the structural integrity of your home vary. Regardless, all basement cracks should be repaired. For more information, contact A-1 Foundation Crack Repair.