After months of high earthquake activity, a fissure opened up near the southwestern tip of Iceland on March 19, 2021. Over a period of about seven months, several other fissures opened up, generating lava flows several kilometers long that filled several valleys and created a new 150-meter high mountain, a sort of mini-shield volcano. The eruption has been intensively studied by geologists because it is the first eruption of its kind in Iceland in living memory, and also because it’s extremely accessible – just a short drive from Reykjavik. Ed Marshall has made dozens of visits to the eruption site to sample the lava.  He then performs geochemical analyses in his lab which show that the magma originates from the very bottom of the crust where it meets the convecting mantle.  Such eruptions generally only occur at mid-ocean ridges, so this is a rare opportunity to study what is happening on the crust-mantle boundary.  It appears to be a place where heterogenous batches of mantle are mixing vigorously, injecting rapidly changing melts into the conduit carrying the magma to the surface.  Ed Marshall is a Postdoctoral Research Fellow at the University of Iceland.