Holzmaar, Volcanic maar lake in Gillenfeld, Germany.

Holzmaar is a maar in the Volcanic Eifel, almost halfway between Gillenfeld and Eckfeld. It measures about 6.8 hectares, with a diameter of 325 metres and a depth of 21 metres, and lies in a nature reserve almost entirely surrounded by woods. A headstream of the Sammetbach crosses the lake, and the Dürres Maar lies close by. Its south and southwest shores have silted up with sediments.

The Holzmaar's sediments date back 23,200 calendar years before present, as established by comparing its sequence and radiometric dating with the Meerfelder Maar. Three dust-rich layers in the sediment record may correspond to ice advances of the northern German inland ice sheet, potentially allowing precise dating of terminal moraines there. The varve chronology's timing of the last glacial maximum agrees closely with GISP2 data but differs somewhat from GRIP.

The German Research Center for Geosciences in Potsdam conducts regular studies at Holzmaar to analyze water parameters and sediment composition.

The maar lies in a nature reserve almost entirely ringed by woodland, with the Dürres Maar immediately next to it. The Sammetbach, a headstream that crosses the basin, feeds the lake. The southern and southwestern shores are silted up with sediments, so open water is reached from the other sides.

In the sediment sequence, three layers unusually rich in dust were found. If these layers match the ice advances of the northern German inland ice, comparing them with the precisely dated Holzmaar dust could allow equally precise dating of terminal moraines in northern Germany.