Lower Tama Lake

There are at least six or seven large explosion craters clustered near to each other on Tama Saddle, between Ruapehu and Ngauruhoe, including craters now filled by the Upper and Lower Tama Lakes. These were active about 10,000 years ago (which is younger than the last ice age / glacial maximum) and are in the low topography away from the main mountains, which explains why they haven't been eroded by glaciers.
Lavas near this location, that form the southern rim of Lower Tama Lake, were sourced from Mt Ruapehu about 50,000 years ago. Those that make the cliffs further to the north and around Upper Tama Lake were erupted as far back as 180,000 to 250,000 years ago.
All these older lavas were already heavily eroded by the time the explosive eruptions occurred in the saddle area. The area surrounding the lakes up to about 3 km away is blanketed by volcanic (pyroclastic) material ranging in size from large blocks of andesite to ash, blasted out of the ground as the craters were formed. Taupo, Ngauruhoe, and (most recently) Ruapehu, have all erupted later on, adding a cover of younger ash deposits.

Lower Tama Lake is accessible from different directions, but a short walk from the Northern Circuit track will take you to a good viewpoint over the lake, You can see that the lake is gradually being filled by sediment that is forming a delta on its northern side. This material is brought in via the adjacent crater by a stream flowing down to Tama Saddle from the south west. The Tama Saddle / Northern Circuit track crosses this stream valley not far to the west of the lake. How many other craters can you see from here in total? If you decide to explore the area more widely, keep a look out for circular depressions that may be old, less distinct craters. The high ground just south of the Northern Circuit track is lava that erupted from Saddle Cone, a crater on the slopes of Ruapehu about 3km to the south.