dyke

laccolith

sill

trap

vent

volcanic neck

 

Modern lava flow on Hawaii.

USGS photo by  J. Kauahikaua

 

 

 

 

 

 

 

 

 

Ancient lava flow at Long Row, Arthur's Seat.

Dipping basalt forms trap terrain

Holyrood Park geology

Lava flow

Definition: a stream of magma discharged on to the ground surface from a volcanic vent or fissure

Lava flows give primary landforms around volcanoes, vents and fissures. Typically, the flows are lobate, with a slag-covered surface of ankle-snapping irregularity. However, the length and form of any flow will reflect the cooling rate and viscosity of the lava, the gradient and the rate of magma discharge.

Lava flows may continue to be expressed in the relief long after volcanic eruption has ceased as secondary landforms. In the Carboniferous rocks of Edinburgh and East Lothian are included thick sequences of stacked lava flows erupted between 400 and 300 million years ago. These mainly basaltic lavas tend to resist weathering and erosion better than the surrounding sedimentary rocks and so form positive relief. Where the lavas are horizontally  or gently inclined then trap landscapes are formed.