GLOSSARY – E
by: Charles O’Dale
EJECTA
Solid, liquid and vaporized material ejected from an impact crater during its formation.
- Distal – Impact ejecta found at distances greater than 5 crater radii from the rim of the source crater;
- Proximal – Impact ejecta found up to 5 crater radii from the rim of the impact crater;
- Blanket – A generally symmetrical apron of ejecta that surrounds an impact crater; and
- Curtain – Impact-excavated clasts ejected ballistically on parabolic trajectories combine into a cone-shaped curtain, the ejecta curtain, expanding outward from the crater rim and turning into the ejecta blanket around the crater.
[see – EJECTA]
ELASTIC REBOUND
Part of a theory explaining the forces that cause earthquakes. In impact cratering , elastic rebound describes the readjustment of the highly compressed floor of the transient cavity in the modification stage.
EUCRITE
A common class of achondrite meteorites composed of pigeonite and plagioclase. These meteorites formed as basaltic flows on a parent body, probably asteroid 4 Vesta. (Data collected by NASA’s Dawn Mission, in orbit around Vesta from 2011-2012, strengthed the association between Vesta and eucrite meteorites.)
EXCAVATION STAGE
The crater excavation stage (Melosh, 1980) overlaps somewhat with the compression stage and involves two processes:
- upward ejection (spalling) of large near-surface fragments and smaller ejecta (ejecta curtain);
- subsurface flow of target material to form the transient crater.
[see – CRATER CLASSIFICATION – Complex crater]
[see – CRATER FORMATION]
[see – CRATER IDENTIFICATION]
EXTINCTION vs IMPACT
Extinction of many groups of organisms at a particular time by environmental catastrophe related with collapsing ecosystems. There are strong indications that some mass extinctions may be caused partly or completely by large asteroidal or cometary impacts.
[see – EXTINCTIONS]