 This is part two of this week's tutorial, and there are two points to this tutorial piece. One is to give you some notes to help you get through the video that we required, and second is to make very clear the specifics on the assignment that you have for this week. Please watch five minutes of the Volcanic Evolution of the Pacific Northwest, and I'll supply a link to it, but there is the YouTube link should you need to upload it again yourself. The first minute or so of the video starts with a summary of the volcanic evolution of the Pacific Northwest and the tectonic settings. It shows the modern landscape features that should be pretty familiar to you already, the Pacific Ocean and the Wanda Fuka Oceanic Plate, the location of the subduction zone itself leading to the Cascades volcanic arc. In addition, you'll see the Yellowstone hotspot, and then they'll talk a little bit about the basin and range extensional province. Suffice to say that's an extensional area, but we know that extension brings basalt lava to the surface, just like it does in oceanic environments that will do it here in the continent, but we're not going to be spending a lot of time on that. And finally, you'll see the Mendocino Triple Junction, which again should be familiar to you. So finishing the first minute of the video talks about the subduction of the Feralon Plate and the jamming of that subduction environment by the accretion of the oceanic Selecia terrain. We then see the jumping jump that happens over millions of years, the relocation of the subduction zone to the west, the profound unhappiness of the abandoned Feralon slab. The peeling of the Feralon slab I find very difficult to envision despite the images in the video, and I'll try to show you a slightly different view of that, because it's a very important process, but like everything else in geology, it happens in three dimensions and over time, so I think a lot of people, including myself and the students that I've worked with in the past, find it confusing. Another thing that I think is a little confusing in this first minute is that the orange color when it spreads out over the landscape indicates calcalculin or arc-like volcanics. So here is a graphic that I've taken from an article on the origin of the Columbia River flood basalts. The figure is really nice in that it shows changes in process over both space and time. The image on the left is color-coded by age, so that things that occurred 17-ish million years ago are shown in pink, and then pink, red, green, purplish down to black, the time gets closer to the present, ending at about 13 million years. The areas on the right part of the figure itself that are shaded in, those blobs, are the projection to the surface of the earth on the hole in the descending pherlon slab. So what I've tried to show you on the right is how that made sense to me. The size of the oval indicates the size of the gap or the tear in the slab, the color of the oval indicates the age, and I've just sort of stacked the ovals on the right to show an age progression even though every one of them is taken at a depth of 70 kilometers. So the hole in the gap in the pherlon slab evolves from something very small that is in one place to something that is much larger and asymmetrical relative to the position of the first hole, and maybe that helps you understand it, I hope so. As we work towards finishing minutes two to three of the video, don't worry about the alkaline lavas as compared to the basalts and basalt agandasites mentioned at time slot one minute and 50 seconds and the back arc versus fore arc sequences. What I want you to know is that the widening arc produces ignembrites which are explosive felsic lavas which are what scatter ash all over. The onset of basalt volcanism related to the Yellowstone hotspot at 17 million years ago is important, and this part of the video really digs into the onset of that hotspot volcanism. Again, what's confusing and this is really confusing in geology is that the age patterns that we see of the volcanic rocks in this area are not what we would expect. You'll notice that the pink and red and the orange and then yellow blobs indicate the different ages of the volcanic rocks, two and three quarters to just over three minutes, and the explanation for this observed pattern, which immediately follows, thank goodness, is valuable. When we've seen in the past projections of the Yellowstone hotspot tracks, they've emphasized only the younging over to the east and not talked about the confusing part, which is the concomitant younging over to the west. When you get to finishing minutes four to five of the video, you'll find that that tectonic explanation uses a lot of colors, and they sort of pop in and spread over the landscape with a little explanation. Just to keep it in perspective, blue is generally used in this video for basalt volcanics, and the warmer colors indicate the more evolved lavas, the andesites through the rhyolites. They've chosen green for the Cascades arc, which is basaltic andesite to andesite in composition, which is a little bit of a change up, but I hope you can keep track of it. So as we move to the activities for the week, your assignment is twofold. I want you to complete a graphing activity that we've uploaded about Hawaiian and Indonesian volcanics, and there are two goals of this activity. The first is to drive home the differences between arc and hotspot volcanic age progressions. The geographic and temporal scales of volcanism can be large, and it's easy to get confused, particularly in areas complicated to the Pacific Northwest, so there's sort of a pedantic, hit you on the head, drive home this relationship piece of the activity. The other aspect of it, though, is a little bit perhaps more subtle, and that is I really want you to hone your skills with Excel. Graphs and figures are the primary ways through which we communicate our data and our interpretations, and for the rest of your career, you're going to need to produce publication quality graphics, so I want you to start now. So the activity includes hand typing in some data and then proving that you are smarter than Excel, and I guarantee you you are, in making beautiful graphs of the same kind of quality that you would want to see if someone gave that to you. So that's really the challenging piece of the assignment. In addition to that bit, I'd really like you to write up a couple questions that point out something that confused you in the video or in this week's presentation, or maybe something that perhaps piques your interest for the coming weeks, so that I can learn from you about what may have been confusing, and then we can have a class discussion about it. If you have questions about the assignment, just shoot them to me via email, and I'll develop a drop box for you to hand it in. Thanks so much. Have a good week.