The Federal Reserve Bank of New York reports that mortgage debt that Americans owe to lenders is at the highest levels in four years during the first quarter of 2016. Total nationwide mortgage debt rose $120 billion from the fourth quarter of 2015 to the first quarter of 2016, for a total of $8.37 trillion.Overall housing debt, which includes home equity lines of credit (HELOC), is now at $8.85 billion. When taking into account mortgage debt, HELOCs, student, auto and credit card debt, the sum total is $12.25 trillion. The Federal Reserve Bank of New York's Household Debt and Credit Report provides unique data and insight into the credit conditions and activity of U.S. consumers.Mortgage application volume rose in the latest week as would-be borrowers continue to take advantage of the low interest rate environment. The Mortgage Bankers Association (MBA) reports that its Market Composite Index, a measure of total mortgage application volume, rose by 2.3% in the latest week, while the refinance index edged higher by 0.4%. The big push came from the purchase index, rising 5%. An MBA spokesperson said, "Purchase applications got back on track last week, resuming the level of activity observed throughout most of April and May.