Geoscience Reference
In-Depth Information
Did dinosaurs ever cause landslides? The short answer is “yes,” although it should
befollowedupbyanotherquestion:“Whatdoyoumeanby'landslide'?”Inpopular
vernacular, this term refers to any movement of earth material, but most often con-
jures visions of a chaotic mass of rocks rapidly moving down a slope, perhaps to-
ward a village, often preceded by a distant rumble and someone yelling dramatic-
ally,“Landslide!”or“Avalanche!”Butgeologistsactuallyapplythesetwowordsto
different mass movements of earth material: a slide moves along a defined plane,
whereas an avalanche is a chaotic flow of rocks and air. Hence, the latter is the sci-
entifically correct warning in this example, which is good to know as it prevents ar-
gumentswithgeologistswhomightobjecttoyouruseof“landslide” asadescriptor
while you are in a village being destroyed by an avalanche.
Anyway, back to dinosaurs and their effects on mass movements. In an article
by geologist David Loope published in 2006, he showed how Early Jurassic dino-
saurs caused sand-dune surfaces to collapse as they walked across them. These an-
cient wind-blown dunes are preserved in the Navajo Sandstone, an Early Jurassic
(190-180
mya
) formation that is well exposed in many national parks of Utah and
other spots in the western U.S. This formation is best known for showing off its
spectacular
cross bedding
, which is the internal structure of sand dunes formed by
Jurassic winds, its beautifully curved, parallel, and intersecting lines only much
laterbecominginertsubjectsofclichédlandscapephotography.Fortunatelyforich-
nologists, the Navajo Sandstone also holds tens of thousands of dinosaur tracks. In
contrast, dinosaur bones are rare in the Navajo Sandstone, so these tracks show that
dinosaurs were there, which ones were present, and what they were doing.
In Loope's study, he looked at an area on the Arizona-Utah border that was
particularly rich in dinosaur tracks, most of which were from variously sized thero-
podsbutalsoincludedprosauropods.Thetrackscouldbeobservedbothonbedding
planes and in vertical sections, which helped to define just how much the dinosaurs
weredisturbingthesanddunesastheywalkedonthem.Perhapsthemostsurprising
conclusion of his investigation was that many of the dinosaur tracks had been made
