Officials in Meridian, Mississippi, are trying to determine what caused a massive gash -- longer than a football field -- to tear through an IHOP parking lot, swallowing more than a dozen cars in the mud below.The parking lot cracked open Saturday night, terrifying the crowd in the busy restaurant."One of the employees ran over to the window and yells ' Earthquake ,'" said Noah Mathis, who was in the restaurant when it happened. "Everyone went into a panic."Although slabs of concrete ripped open, creating the massive crevice 15 feet deep, no one was hurt."Everything was sudden and quick," Mathis said. "They were slamming their forks down from eating and they were sprinting outside as quick as they could."Emergency personnel said an underground drain pipe collapsed, but it was not clear why. Officials say the investigation has not ruled out the possibility that construction at the newly opened IHOP played a contributing factor.