lava tree mold
{{Short description|Geologic feature}}
File:Nisga'a Memorial Lava Beds Provincial Park tree mould.jpg lava flow]]
A lava tree mold, sometimes erroneously called a lava tree cast, is a hollow lava formation that formed around a tree trunk. They are created when lava flows through an area of trees, coating their exterior. The lava cools just enough to create a solid crust around the trunk, but the tree inside burns away leaving a cavity.{{cite book |title= Hawaii and its volcanoes |author= Charles Henry Hitchcock |publisher= The Hawaiian Gazette Company |year= 1911 |url= https://archive.org/details/hawaiianditsvol01hitcgoog |quote= rufus lyman. |pages=[https://archive.org/details/hawaiianditsvol01hitcgoog/page/n214 147]–148 |edition = second }} Molds of trees may be vertical or horizontal.{{cite book|last1=Green|first1=Jack|last2=Short|first2=Nicholas M.|year=1971|page=418|title=Volcanic Landforms and Surface Features}} In many cases, mold formation requires slow moving lava, as well as enough time for the mold to chill.
Methane explosions
A unique phenomenon may occur during the formation of vertical tree molds. As the lava-encased tree burns away, the roots are heated up and generate a "producer" gas, such as methane. If the roots penetrate into a cavity, such as a lava tube or tumulus crack, it may come into contact with oxygen. Because there is a source of heat already present, the charred root or the lava itself, a methane explosion may follow if the oxygen and producer gas mixture is between 5 and 15% (volume-percent fuel).{{cite web |title= 'Methane' explosions - a volcanic hazard worth understanding |author= USGS |publisher= USGS |date= 2002-10-17 |url= https://volcanoes.usgs.gov/observatories/hvo/hvo_volcano_watch.html?vwid=731 |accessdate =2019-09-21 }}