Columnar Basalt at Latourelle Falls

• As lava cools, it forms a dark gray rock called basalt. As basalt lava erupts from volcanic vents and cools, it shrinks and cracks. Sometimes vertical columns form. Well developed columns result from homogeneous lava cooling at a uniform rate.  
• If you look closely at the columns here (in middle of picture), you might notice it is divided into two parts.  At the bottom, the lava cooled slowly forming regular, widely spaced columns.  Higher up, it cooled rapidly creating a jumbled looking mass of irregular, closely spaced columns. As you look for lava layers today at Latourelle Falls, Multnomah Falls and the Oneonta Gorge, notice that many quite dramatically contain columnar basalt.  

Latourelle Falls & Columnar Basalt —
​Attribution: Gary Halvorson, Oregon State Archives