Conflicting Viewpoints and Hypotheses

Two scientists debate the formation of the Grand Canyon.

Scientist 1
The Grand Canyon was carved slowly over approximately 6 million years. The Colorado River gradually eroded the uplifting Colorado Plateau. The erosion rate remained relatively constant, averaging about $0.15\text{ mm/yr}$. This slow process allowed the river to gradually cut through the rising rock strata, depositing fine, well-sorted sediments downstream at a steady rate.

Scientist 2
The Grand Canyon was formed rapidly, likely within a few weeks, by a catastrophic outburst flood. Approximately 5.5 million years ago, a massive prehistoric lake located on the Colorado Plateau breached its natural barrier. The sudden release of water created a massive, high-velocity flow that carved the canyon. This flood would have deposited a thick layer of unsorted gravel and large boulders downstream.

Based on the presented viewpoints, the discovery of a downstream sediment layer containing large, poorly sorted boulders dated to 5.5 million years ago is consistent with the predictions of Scientist 1.

### Hawaiian-Emperor Seamount Chain

The Hawaiian-Emperor seamount chain is a trail of volcanoes on the Pacific Plate. Two hypotheses discuss the origin of these volcanoes.

Hypothesis 1 (Stationary Plume)
A stationary mantle plume under the Pacific Plate supplies magma. As the plate moves northwestward at a constant rate, new volcanoes form directly over the plume. Volcanoes that have moved away from the plume become inactive. This hypothesis predicts that the age of the seamounts increases linearly with distance from the active hotspot ($0\text{ km}$ at Hawaii).

Hypothesis 2 (Lithospheric Stress)
Volcanism occurs along pre-existing fractures in the plate. The fractures open due to tectonic stress changes at plate boundaries. Volcanic activity can occur simultaneously along a fracture zone, and the age of volcanic centers is determined by when stress reactivation occurred, resulting in clustered or non-linear ages along the chain.

Researchers measured the age and distance from Hawaii of four seamounts in the chain, shown in the table below:

Which hypothesis is supported by this data, and why?