The Leirhnjukur area is a central volcano with absolutely relatively new barren lava fields, where the Apollo 11 crew, came in the late 60's to train for their impending moonwalks.
From the parking area near Mt. Leirhnjukur lies an easy trail to the mountain. The route then leads through a hot spring area, into craters formed in the Krafla fires and to the summit. From there the route lies back to the parking area. Altogether hike takes one to one and a half hours.
A trail lies between the information center in "Reykjahlid" and Mt. Leirhnjukur. It lies from the Leirhnjukur and through a crater area. From there, the route continues through lava and gravel banks to "Mt. Hlidarfjall", along the bank of the river "Elda" back down to the information center. The "Mt. Krafla" route takes 3-4 hours to walk and is fairly easy.
"The Myvatnseldar" eruptions (the “Myvatn fires”) in 1724 began with a great volcanic explosion which formed the crater "Stora - Viti". In the following years, a series of earthquakes and eruptions occurred in the vicinity of "Krafla" mountain. The greatest eruption took place in 1729, when lava flowed from Leirhnjukur mountain down to Myvatn lake. "Eldhraun", the lava field formed during the eruptions. A new series of eruptions (the "Krafla-fires") began in Krafla in 1975, after an intermission of about 250 years. In the following nine years, nine eruptions occurred.
One hundred thousand years ago, there was a volcanic cone here that caved in after erupting. The caldera thus formed is now filled with younger volcanic material. Below at a depth of about 3 km, however, is a magma chamber. Volcanic activity in the area occurs at intervals of several centuries.
Magma flows into the chamber, which expands and raises the ground. The chamber then bursts and magma flows through underground fissures to the north or south. A part of the magma may then surface in an eruption. As the pressure in the magma chamber decreases, the land subsides quickly. This process repeats itself every few months for several years running.